[Spaceships] Designers' Championship I: ground to LEO
 

Using the spaceship design rules in GURPS Spaceships, without superscience, what is the cheapest way to provide a shuttle service between the ground and low Earth orbit, at TL 9? At TL 10? At TL 11?

Ground rules:

1. Orbital lighters must not release highly-radioactive exhaust into Earth's atmosphere.
2. Lighters must carry their passengers from a spaceport on Earth's surface to a ship or space station in a ninety-minute prograde equatorial orbit (ie. at an altitude of 170 miles, heading east at circular orbit velocity), and then return to a spaceport on Earth's equator. For simplicity, treat the circular orbit velocity at LEO as 4.85 miles per second, and the rotation of the Earth as providing 0.25 miles per second, requiring the engines to provide 4.6 miles per second of delta-v to do the job.
3. Earth may be assumed to have no more than two suitable spaceports, one in Ecuador at an altitude of 15,000 feet and possibly one on Sumatra at 9,000 feet. Headway on the service must therefore be an integer multiple of 45 minutes.
4. Embarkation and disembarkation may be assumed to require ten minutes each, and refuelling (if necessary) may be assumed to be completed within twenty minutes, so that the lighter must spend 20 minutes docked to the ship and twenty minutes on the ground in each duty cycle.
5. A lighter may be assumed be in service for 7 300 hours per year.
6. Lighter crew work 1,920 hours per year, of which 5% is administrative overhead, so the flight crew wage bill for the operation is wages for four crews.
7. Lighter crew is a comfortable job.
8. Lighters work at an average load factor of 75% (ie. on average, quarter of the seats are empty).
9. The commercial real return on capital is 5% per annum.
10. Depreciation on an orbital lighter is 4% per annum, straight-line (for accounting convenience).
11. Basic insurance of an orbital lighter is 1% per annum. Operational insurance is 0.001% per round trip to orbit, times 3 if the lighter's Hnd is +3, times six for Hnd +2, times ten for Hnd +1, times 15 for Hnd +0.
12. The servicing cost on an orbital lighter is 0.01% of the cost of engine and fuel tanks, per round trip.
13. Fuel costs are as given on Spaceships p. 46.
14. In the case of a vehicle that is not winged, it will be assumed that supporting the vehicle against gravity will reduce available delta-v from V to V' = V * {square root of (A-squared - 1)} / A, where A is the acceleration of the vehicle.

What is the most cost-effective ground-to-orbit lighter you can build at each TL, without superscience?

How are things different on a backwoods colony planet where there is only a liner in orbit 10% of the time, and where there is only one spaceport?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

By the way: is there any comment on the ground rules as set out?

How do wings affect Hnd?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

What about a space lift?
Is that super science?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Space lifts are easily TL 9, given an adequately motivated and organized civilization.

A launch loop might be even cheaper than that, though.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

• There are no rules for them in GURPS Spaceships, so they don't provide a suitable basis for a design championship.

• Space lifts are no good for getting to LEO: you can't get off below GEO. And it takes a long time to get to GEO, which might make space lifts unattractive to passengers. Rotorvators, bolo space stations, and even space fountains sound more practical to me.

• Space lifts eat up an awful lot of valuable territory in orbit, besides which they are mind-bogglingly capital-intense, and a very considerable engineering challenge. A beanstalk is equivalent to a suspension bridge with a 24,000-mile span. There might be a long wait before we get one built. We are much closer to building an orbital lighter. It is not clear to me that a space lift will ever be economic: operating costs are much lower than shuttles, but amortisation is through the roof, and there might be prohibitive rental costs on orbital territory.

• Until we design the most cost-effective orbital lighter we don't know what price the space lift will have to compete with. I won't be surprised if at higher TLs lighters (perhaps fusion powered) provide a trip to LEO that is cheaper than a space lift ticket to GEO.

• This design exercise will give us a basic approach to the more general problem of building lighters for trips from ground to low orbit on habitable planets. This will be important in the case of comparatively low-population colony worlds, which don't generate enough traffic to amortise a minimum-scale beanstalk.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Laser Launch system is the most cost effective(at low TLs), I believe, but that was in THS, not Spaceships.

Also, by highly radioactiv,e do you mean no orion drives, or no saltwater nuke drives? Orion drives are not that hazardous in terms of fall-out

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I was particularly thinking of NSWR. Old Bang-Bang hadn't even crossed my mind. I think Orion is currently outlawed by the CTBT, but I might entertain a case that the law might be reformed if the emissions were likely to be negligible.

I am, obviously, considering commercial operations: thousands of passengers per day. Regulators would be concerned with cumulative emissions over myriads of launches, plus of course the possible use of the bombs as bombs.

Have you thought about Daedalus?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

The trouble with any sort of pulse system especialy the Daedalus fusion pulse system is the expense of the fuel, I don't currently own spaceships but I suspect that this will prove to be the killer for any sort of Orion/ Daedalus pulse engine in regular service. As the rules of the competion, if not the build system, appear preclude hybrid vehicles such as the Helios designs (two stage vehicles using a chemical first stage and a nuclear second stage) at least at TL 9, nuclear systems may not be all that credible for low tech levels.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Which is not a problem for this exercise: you only have to calculate it, not pay it.

It is more or less necessary for participation in this designers' championship.

The PDF is US$9.95, plus which printing and binding my copy cost me about US$4.90. I consider it to have been worth every penny.

The build system certainly doesn't preclude staged vehicles. As for the rules of the competition, if they rule out an economic and practical approach I would be open to changing anything that was unreasonable or opening a Designer's Championship Ia with more relaxed rules.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

The PDF is something I am going to get as of payday (the joys of being a student again- only so many hours a week you are physicaly able to work work etc). My coment about the Helios design (nominaly TL 7- at least when it was first proposed) being useless was not about staging but the emmisions problem, using the chemical stage to reach the stratosphere and then using a nuclear sustainer to finish the job seams to violate rule 1 quite thouroughly. Even a closed cycle engine is probably a dead end because of its low thrust, without TL 10+ fusion systems it isn't going to fly.
As of when I get a copy I will try runing up stats for one of the Helios RLV designs using TL 9 materials and components while it will almost certainly not be legal under the competition rules (or sane for that matter) it may provide a useful reference.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Don't mind sanity too much. I am a Girl Genius fan. My motto is "What would Baron Wulfenbach do?"

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Reaction Engine, Laser Rocket (TL 9) [REAR]

Laser rockets uses a ground based laser battery that evaporates reaction mass producing thrust. Each Laser Rocket engine must be powered by a laser battery, 10 GW for sm+5, 30 GW for sm +6, 100 GW for sm+7, 300 GW for sm+8 etc (the standard 1-3-10 progression). Each engine produces 2G of thrust, and each fuel tank of ablative plastic propellant gives 0,45mps of delta-V.

Cost for the spaceship part of the engine is as a chemical rocket of same size, ablative plastic costs $200/ton.

This is the Laser Launch Engine system as converted by Boobis, and numbers double checked by me. Mind if we use that?

Main cost of launch is in the ground based power station, and a dedicated nuclear reactor should produce enough juice to send up a flight every five minutes.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I'd certainly like to see how it comes out. If necessary we can hold a separate contest to design an orbital lighter for use on backwoods colonies, as a landing boat for exploration ships, etc.

Assume 10% per annum cost of capital (depreciation plus insurance plus interest), and that ground workers have average jobs. 1/6 down time for maintenance.

The big issue might turn out to be getting enough traffic to keep the load factor up. Assume a 75% load factor, but keep an eye on passenger numbers: if you start pushing a billion passenger movements a year that might be a problem.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Well, you wire the plant into a local grid, any time traffic drops, you sell power output on the market for ground-based power

Re: [Spaceships] Designers' Championship I: ground to LEO
 

That will help amortise the generator, but not the laser.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Lasers. You build about 40,000 small ones, so you have exceptionally high reliability. Even if somehow, 5% of the lasers failed all at once, there would probably still be enough to get your payload in orbit, and you can do maintenance on the lasers without stopping launches. Plus, building one huge laser is much more expensive/technically difficult. And if you want to scale up your payload that you can launch, you just build more lasers.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

What do you mean by "cost effective"?

I would normally calculate Return on Investment. So build cost may be only a small consideration.

What ticket price can we charge? (what will the market bear?)

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Do you mean a backwoods planet with exactly the same stats as Earth? Or did you have a particular planet in mind, like the trace atmosphere and low gravity planet Mars? Or can we make up a planet to best fit our designs?

Hmm, this seems like two different competitions.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I mean "having a high ratio of effect achieved to cost borne", or, which is the same thing, a low ratio of cost to effect.

What is (at each TL) the shuttle that has the lowest ratio of total cost (ie. operating costs plus amortisation of investment) to the number of trips to orbit that it provides?

Include operating costs, such as maintenance, fuel, and wages.

Assume that you are in a competitive industry that is in long-run equilibrium. You cannot charge a higher price than your competitors, and they cannot charge a price lower than their costs including amortisation. Ticket price will be equal to cost at the stated price of capital.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Take Earth as a representative habitable planet. In other words, take the planet as having the same characteristics as Earth except that its traffic will not support a full-time round-the-clock shuttle service.

It is. The 'how are things different' bit is an afterthought, not of the essence.

The essence is to establish what the price of a ticket to/from orbit is likely to be for a developed planet.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I am guessing that a 6G laser launcher (5G effective) with 13 fuel tanks and 2 passenger seating will be the one to beat.

Is there a limit on the G force we can apply to passengers?

Do we need to worry about the real G Force felt with nearly empty tanks?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

With a laser launch system I guess you have to stay over the launcher, which is a bit of a pest. With a 6 g rocket you would pitch down to a flight path with a 9.6° angle of climb, and enjoy an effective acceleration of 5.9g. But that gets you over the horizon pretty quickly. (The advantage of an inclined flight-path is more significant with lower acceleration: at 2 gee it means a difference of 70% in your available delta-v).

I have some sort of hopes for air-breathing fusion engines at the higher TLs, maybe even air-breathing AM engines at the lower ones.

Crushing the passengers to death is counter-indicated. And there are brownie points to be had for getting them into orbit without their blacking out. But trying to figure an appropriate cash bonus for an easy ride is too difficult and fiddly for this, which is supposed to be a simple exercise.

I don't think so. All the rocket types we have on hand can be throttled back to allow for the changing mass.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Then I think we need conversions for the fission/fusion air rams from TS.

I got as far as outline design for a laser launch vehicle before deciding that the base station cost is going to be very expensive. Even for a 4G size 5 craft you are looking at M$360+ for the base station.

I now quite like the look of the Nuclear thermal rocket at TL9+. Though not sure if its exhaust is allowed?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

TL9+ Orbital Lighter (Spaceplane) v1 "Alida"

Alida class spaceplanes are cheap reusable single stage orbital lighters that can take off and land at a normal airport.

Using a jet engine to take off it clears local population centres before going supersonic and accelerating to maximum air speed. It then engages the Nuclear Thermal rocket drive and climbs into orbit in under 7 minutes. Having docked and exchanged passengers it reenters atmosphere and then makes a slow descent back to Earth. On final approach it powers up its jet engine and lands at an airport. It can comfortably make the return journey once every two orbits or every 180 minutes. (It could probably make the journey every 1.5 orbits by constantly switching between landing sites in two hemispheres).

Front
1 Armor (Advanced Laminate)
2-3 Passenger Seating (4 seats)
4-6 Fuel Tank (Hydrogen)
0 Control Room

Central
1-6 Fuel Tank (Hydrogen)
0 Fuel Tank (1 hours Jet Fuel)

Rear
1-5 Nuclear Thermal Rocket (2.5G)
6 Jet Engine (1G)

dST/dHP 20, Hnd 4 atmo/0 space, SR 4/5, HT 12, Move 1G/2500 mph/0.69 mps, 2.5G/5.67 mps, LWt 30, Load 0.5, SM +5, Occ 1+4 SV, dDR 3, Cost M$ 1.44, TL9, Streamlined, Winged, Length 15 yards

DeltaV 6.36mps (ample reserve)
-Jet Engine 2500mph = 0.69mps
-9 Hydrogen Fuel Tanks = 9*0.45*1.4 (9 tank adjustment) = 5.67 mps

Draft economics:

1 flight every 3 hours operating for 7200 hours pa= 2400 flights per year
4 passenger seats at 75% loading = 3 passengers per trip
= 7,200 passengers per year

Variable cost per trip:
Insurance = M$1.44/1000 = K$1.44
Servicing = M$1.44/100 = K$14.4
Fuel: 13.5 tons Hydrogen (K$27) + 1.5 tons Jet Fuel (K$6) = K$33

Total Variable = 1.44+14.4+33 = K$48.84

Annual Costs to Amortise:
Requires 4 pilots at $7200 pm TL9 Comfortable salary each = K$345.6 pa
Other economics = Insurance+Depreciation+RoI = 10% = K$ 144

Total Fixed = K$ 489.6

Divided over 2400 trips = $204 per trip

Return Ticket price = K$49 / 3 passengers = $16,350 (4.5 months income for an average TL9 job)

I don't see a significant difference between TLs other than the pilots wages increase, which adds about $30 per TL to the ticket price.

On backwoods world you only employ one pilot part time so annual costs are K$34.56 + K$144 = K$178.56 / 240 trips = $744 per trip

So ticket price per passenger increases by $250 to $16,600 on backwoods worlds

As most of the ticket cost is variable cost the ticket price should scale with ship size fairly linearly.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Inaugural champion designer (div'n I, ground to LEO):

thtraveller

for the "Alida" class orbital lighter (spaceplane)

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Will the "Ram-Rockets" rules on p. 30 do the job?

I would guess so. In the NERVA design the nuclear fuel retained in the core. The propellant should not pick up significant radioactivity as it passes through as coolant: indeed, hydrogen cannot.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Shouldn't we wait and see if others post a design?

Oops missed that option. In which case the Alida does not need a Jet Engine and Jet fuel and can now operate from any airport in the world (not just those near the equator).

Just convert the Jet Engine to a NT Ram-rocket, lose the jet fuel tank, add a passenger seat module (+2 seats). Cost is now M$ 1.89. Return Ticket Price is now $10,640 (3 months basic income). Now has 3G drive to orbit, Top Air Speed 1800 mph (0.5 mps).

Re: [Spaceships] Designers' Championship I: ground to LEO
 

TL9+ Orbital Lighter (Spaceplane) v2 "Alida"

Alida class spaceplanes are cheap reusable single stage orbital lighters that can take off and land at a normal airport anywhere in the world.

Using a Nuclear Thermal Rocket in fuel-less air-ram mode to take off it clears local population centres before going supersonic and accelerating to maximum air speed in an easterly direction. It then engages the other normal Nuclear Thermal rockets and climbs into orbit in under 6 minutes. Having docked and exchanged passengers it re-enters atmosphere and then makes a rapid descent back to Earth. Again using its air-ram engine it lands at an airport. It can comfortably make the return journey once every two orbits or every 180 minutes. (It could probably make the journey every 1.5 orbits by constantly switching between landing sites in two hemispheres).

Edit: The excess delta-V (6.17 mps versus the 4.6 mps required) allows for losses due to air-resistance and gravity. It also includes an emergency reserve (e.g. single engine failure in flight). The 3G thrust allows it to get it into orbit quickly to reduce gravitational losses.

Edit: The excess delta-V also allows for the spaceplane to enter orbit from higher latitudes rather than on the equator (e.g. Europe) and hence not have the full benefit of 0.25 mps from equatorial spin. It also allows it to enter slightly higher orbits and also satisfies the G:Spaceships 5.6 mps orbital velocity requirement.

Front
1 Armor (Advanced Laminate)
2-4 Passenger Seating (6 seats)
5-6 Fuel Tank (Hydrogen)
0 Control Room

Central
1-0 Fuel Tank (Hydrogen)

Rear
1-5 Nuclear Thermal Rocket (2.5G)
6 Nuclear Thermal Ram-Rocket (0.5G)

dST/dHP 20, Hnd 4 atmo/0 space, SR 4/5, HT 12, Move Fly 0.5G/1800 mph/0.5 mps, Boost 3G/5.67 mps, LWt 30, Load 0.7, SM +5, Occ 1+6 SV, dDR 3, Cost M$ 1.89, TL9, Streamlined, Winged, Length 15 yards

DeltaV 6.17mps (ample reserve)
-Ram Rocket 1800mph = 0.5 mps
-9 Hydrogen Fuel Tanks = 9*0.45*1.4 (9 tank adjustment) = 5.67 mps

Economics:

1 flight every 3 hours operating for 7200 hours pa= 2400 flights per year
6 passenger seats at 75% loading = 4.5 passengers per trip
= 10,800 passengers per year

Variable cost per trip:
Insurance = M$1.89/1000 = K$1.89
Servicing = M$1.89/100 = K$18.9
Fuel: 13.5 tons Hydrogen (K$27)

Total Variable Cost = 1.89+18.9+27 = K$47.79

Annual Costs to Amortise:
Requires 4 pilots at $7200 pm TL9 Comfortable salary each = K$345.6 pa
Other economics = Insurance+Depreciation+RoI = 10% = K$ 189

Total Fixed Cost = K$ 534.6

Divided over 2400 trips = $223 per trip

Return Ticket price = K$48 / 4.5 passengers = $10,640 (3 months income for an average TL9 job)

I don't see a significant difference between TLs other than the pilots wages increase, which adds about $30 per TL to the ticket price.

On a backwoods world you only employ one pilot part time so annual costs are K$34.56 + K$189 = K$223.56 / 240 trips = $932 per trip

So ticket price per passenger increases by $210 to $10,850 on backwoods worlds

As most of the ticket cost is variable cost the ticket price should scale with ship size fairly linearly.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Is that meant to be all divided by A? Otherwise Delta-V increases significantly when you take the wings off.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I reckon that you can be acknowledged champ until someone posts a better design (if anyone does).

Re: [Spaceships] Designers' Championship I: ground to LEO
 

So it is. My mistake.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Funny, i did an almost exactly equivalent design, including going from jet assisted to ramjets when spaceships was released, but I have since thrown out my notes. Cool that you actually did a design, myself I really don't grook the eco-speech in the ground rules.

Since cost mostly is from fuel, it might be cheaper to have more engines as ram-jets. You would be saving 0,58 mps worth of hydrogen each trip if you used three ram-jets, costing M2,4 extra. Also do you really need 3G's accel? Reducing to 1,5G gives you twice the amounts of passengers though I don't know what that will do with the timing-calculations from the ground-rules, but since T is k/A for some k (p. 37) we should be roughly doubling the to-orbit time, and I don't think 6 or 12 minutes will matter (but hey, I really don't understand much of the ground-rules).

So shamelessly building upon your design I would do the Alida mk Boobis with three ram-jets and 6 passenger modules. Hoping that almost tripling the price of the shuttle and increasing to-orbit time with 6 min would pay of.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Note: I'm to lazy to do an actual complete design, but I'm tossing out ideas for grabs.

Also while I'm at it you don't really need "Advanced Laminate", and while it won't matter much it will be strictly cheaper if you go with Steel, and you don't need the DR iirc.

Next is the cost of the pilot. While it's a small part you could employ a faux multistage design, doing an sm+5 upper stage without engines that never leaves the sm+6 lower stage. This lets you keep the sm+5 control-room but roughly six times your previous # passengers, giving you more seats/pilot (though I don't know what will happen with seats/shutle-cost). David stated in some post that this should really lower sr/hnd but that might be ok.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Well, you want at least 3G of accel to get out of earth orbit because 1G of that is going to be wasted negating earth gravity, so you can't really afford to drop engines, and, by the rules as written, ram-rockets are pretty expensive. It might make sense to allocate some tankage to water because it's cheaper, but water is going to come out a bit more radioactive, and might kill some of the dV, but it could allow for less engine because of the higher thrust.

Either way, using a standard, hydrogen-fueled jet engine, similar to the original design, allows the lighter to gain more altitude before it engages its fission thermal rockets, which might be more amenable to an eco-sensitive populace.

I've been thinking, too, that it might make sense to use a laser-launch design that uses water as its primary reaction mass rather than ablative plastic. Water would be far less toxic, and is widely available. If, by RAW, water won't give enough isp to attain good dV while carrying enough passengers, hydrogen is probably a pretty good idea too.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

What? IIRC you just need a tiny bit more than 1 G to reach orbit, but it might take a looooong time. BUT you could for example use three engines for 1,5G and still make it out to space quite easily. And with a winged design you can probably argue that you can glide-land on 0,5 G so that gives you the possibility to have 2/3 of your engines faulting. As for tankage, since you can make it out to space on 3 engines but need 9 tanks, reducing dV by increasing thrust seems pretty useless.

Jet engines are not hydrogen fueled. Jet engines are jetfuel-fueled.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Yes, 1.5G is plenty to reach orbit, as long as you have enough dV. As to glide-landing, with a well designed orbiter its theoretically possible with no engines at all working. With 0.5G and a long enough runway it should be easy. A winged design can also increase your fuel efficiency on the way up, unless you launch vertically.

Jet engines are definitely jet-engine fueled. A hydrogen-fueled variant is possible, but the version in GURPS spaceships isn't one.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I think my economics might need revising slightly as the fission air ram is likely to need new fission cores every couple of years. Though ship cost isn't a major factor in the ticket price so likely only a few hundred dollars per ticket increase.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

But it takes a lot longer so you need a lot more fuel. You have gravity pulling down on you the whole time. Worst case is you subtract 1G from your thrust and discount all the delta-V from the fuel that 1G of engine uses for the time it takes you to reach orbit.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Think of it this way - if you have a 1.5 G engine, you're only accelerating at .5G, but still burning 1.5 G of fuel. You can improve efficiency by angling your engine, giving you a maximum of 1G of vertical thrust to cancel out gravity and 1.12G of horizontal acceleration with 1.5 G thrusters, but your dV to LEO would be pretty compromised with only about 75% fuel efficiency... in other words, you'd need to burn about 30% more dV than your orbital velocity. With 3G of acceleration angled properly, you can have 2.83G of horizontal acceleration while canceling out gravity, for an efficiency of 94% - you'd only be burning about 6% more dV than your orbital velocity. Of course, considerations are a little more complicated because you still need to get out of atmo and you suffer from atmospheric drag, but those complications are greatly reduced with jets or ram-rockets to bring you to the top of the atmosphere.

As far as powering jets with hydrogen, a lot of scramjet designs burn H, and I imagine hydrogen will be a more common fuel in a hydrocarbon poor future than standard Jet-A.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Wouldn't they operate 50 years on internal fuel like the TL9 fission powerplants?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Note: I know nothing of actual spaceflight.

While it's neither in RAW nor ground-rules, it seems reasonable to somehow subtract (some factor of) planetary gravity at least when comparing launch-times. But 2G (3-1) is just four times higher than 0,5G (1,5-1) which should make a 1,5G thrust ship viable, shouldn't take more than 6x4=24 minutes, still not that high.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

While I can't say anything about if your right or not, I can say it's neither in RAW nor in the ground-rules.

In spaceships there is no scramjets. You may be perfectly right, but in the contest of the competition it wouldn't be fair to switch jet-fuel for 4K a pop with hydrogen for 2K.

This brings me to my conclusion. The ground-rules need updating. More precise rules for calculating fuel-consumption with/without wings, ram-jets and variable thrust. If there is a ~20-25% increase in fuel-efficiency if you increase thrust from 1,5G to 3G, as your numbers indicate, we need some way of actually calculating that.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

It seems reasonable, but is a flawed reading of the principles. Delta-V is the change in velocity produced by an engine. There is a minimum dV needed to reach a given orbit, or escape a planet altogether. This is the integral or sum of the change in velocity from ground to orbit. The rate at which this change in velocity is achieved is irrelevant, the dV is the same. The dV of an engine is an integral of the change in velocity produced by the thrust, that is the sum of thrust over all the burn time. This is why GURPS Spaceships doesn't talk about the effects of increased acceleration on fuel efficiency in planetary lift-off. As long as you have enough thrust to overcome gravity, its the total Delta-V that counts, and has to be greater than the dV needed to reach orbit.

For comparison, note that a craft with wings or contragrav and only 0.1G acceleration would be able to achieve orbit, given enough dV and patience.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

This is fundamentally misunderstanding the mathematics. Ignoring the effects of wings, the total dV needed to reach orbit is a function of gravity. The design of your craft has no effect at all on the dV needed. If your passengers are patient, 1.1G and plenty of dV is far better than 3G and barely enough dV. Because of the way velocity changes aggregate, the rate of change of velocity does not affect the gravitational effects that have to be overcome. For the same dV, more thrust means that you lose the same amount of gravity (gravitational potential energy) faster. It doesn't mean less gravity (gravitational potential energy).

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Could someone take a look at this draft, for a TL 10 antimatter thermal lighter? All costs are in thousands:

Front
1 Armor (AML/SL) $60 dDR 3
2 Passenger (2) $10
3 Passenger (2) $10
4 Passenger (2) $10
5 Passenger (2) $10
6 Passenger (2) $10
0 Control Room $60

Central
1 AC Hydrogen Fuel $10
2 AC Hydrogen Fuel $10
3 AC Hydrogen Fuel $10
4 Armor (AML/SL) $60 dDR 3
5 Passenger (2) $10
6 Passenger (2) $10
0 Passenger (2) $10

Rear
1 ATR Ram-Rocket $750
2 ATR Ram-Rocket $750
3 ATR Ram-Rocket $750
4 ATR Ram-Rocket $750
5 ATR Ram-Rocket $750
6 ATR Ram-Rocket $750

Winged $150

Thrust 1.2 G SM 5
Air Speed 2739 mph dST/dHP 20
0.76 mps Hnd 4/0
Orbit DV 4.6 mps SR 5/4
Fuel DV 3.84 mps HT 12
Fuel Cost $16.67 $/mps TL 10
Fuel to Orbit $63.99 Loaded Wgt 30 tons
Time to Orbit 10.35 Length 45 ft
Cost $4,940

VC Per Trip Fixed Annual
Op Ins $0.74 Ins $49.4
Service $0.45 Crew $537.6
Fuel $63.99 Dep+ROC $444.6
Total $65.18 Total $1,031.6

Flights/Year 2400
Passengers 12 /trip
28800 /year
Total Costs $157,468
Cost/Passenger $5.47

Re: [Spaceships] Designers' Championship I: ground to LEO
 

<deleted>

I'm sorry, that was uncalled-for.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Notice that if you go straight up the flight path angle is zero, the sine of which is also zero. Then your losses are zero, irrespective of your acceleration. In other words, this is energy used to accelerate your craft horizontally, not energy used to "fight" gravity. The gravitational potential energy of an object in orbit is the same regardless of how it got there. All other things being equal, all you need to give your orbiter is that much energy. Real life is undoubtedly never quite that simple.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

If you go straight up, your flight path angle is 90 (it's measured from horizontal), and your losses are maximized.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Well, if you really want to mess with things, I'm sure we can integrate over the path of the rocket, factoring in losses due to gravity at a given height, losses due to atmospheric drag dependent on speed, latitude, and altitude, and variations depending on the latitude and direction of launch. It would be a good exercise in whether or not I can still calculate an integral that complex, but, we can probably just forget about atmospheric drag if pretty much every design uses a ram-rocket or jet component, and estimating losses due to gravity for LEO insertion is pretty simple too.

I've had another thought too - I'm not sure if it's occurred to anybody to take passenger comfort into account - most people don't appreciate being accelerated at rates approaching 3G for an extended period of time. For example, you don't want to have to resuscitate Grandma on her way to visit her son who's working in Luna-3 Colony. It might be that a slower, though lossier lighter is preferable to a faster one.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I hadn't spotted that. I was taking my figures from VE2/Vx1, but that also has fission reactors requiring a 2 year refuel cycle. So I guess my original figures stand.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

All air-rams too I assume from the cost.

The exhaust during boost is very radioactive. ;-)

The component and total ship costs all look fine.

I don't understand what you are saying here. Antimatter conditioned Hydrogen is 12,000 K$ per ton or 10,000 K$ per mps. Fuel cost is 38,400 K$ to orbit.

You seem to have used a different ship base cost at different points here, and as mentioned above fuel costs are rather high - 3.2 M$ per passenger.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Heh, taking a strict interpretation of the ground rules allows me to build a shuttle with a single 0.5 Fusion Thermal Ram Rocket (0.5 mps dV), 8 fuel tanks (4.32 mps dV), 2 armor, 1 control room, 8 passenger modules (16 seats). This would reduce the return ticket costs per passenger down to $3,150 each. ;-)

Anyway back to "reality".

Note my original design (with 6.17 mps dV) allowed for losses due to air-resistance and gravity (though not a full 1G loss as it is winged) and included a reasonable emergency reserve (e.g. single engine failure in flight). The 3G thrust was to get it into orbit quickly to reduce gravitational losses.

I also thought the excess delta-V would allow for the spaceplane to enter orbit from higher latitudes rather than on the equator (e.g. Europe) and hence not have the full benefit of 0.25 mps from equatorial spin. Or enter slightly higher orbits and also satisfy the G:Spaceships 5.6 mps orbital velocity requirement.

I will add that to the color text.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

What's the go of that? The figure in the OP is slightly too low, but the correct figure for orbital velocity is 7.9 km/sec (4.9 miles/sec), not 5.6 miles/sec (9.0 km/sec). Do you think that the extra 0.7 miles/sec are supposed to cover the gravitational and other losses?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Perhaps, 1 mps seems like a typical loss. You would have to ask the author. It uses a 0.8 * escape velocity = orbital velocity for all the planets and does explicitly mention 5.6 mps for Earth in an example.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Note: I still claim no knowledge in this.

I can't get this out of my head.

I get the fact that delta-V is delta-V and that the amount of delta-V required is constant regardless of acceleration. But it seems to me that the amount of fuel needed to attain a certain amount of delta-V might not be independent of your acceleration.

Using my high-school physics, and an idealized (silly?) model disregarding wings, rotation, rocket equations and angles I get the (quite possibly flawed) numbers:

Unit-engine: 10 kgm/s^2 thrust using 1 l/s of fuel
Ship-mass: 1 kg in total, regardless of engines and fuel left
Fuel: 100 l

Hell, thats some darn light fuel :)

Installing 2 unit-engines in the ship gives me 1 G of net acceleration for 50 seconds, amounting to 500 m/s delta-V.

Installing 4 unit-engines gives me 3 G of net acceleration for 25 seconds amounting to 750 m/s of delta-V.

Now elustran claims

I don't think 75% to 94% is a huge difference, and I interpret various other bits and pieces of information that wings will further reduce the gap in efficiency. If his numbers are close enough I'm starting to believe that we can ignore the thrust-on-fuel-efficiency effect since it ain't _that_ big, and granny doesn't like 3G :)

Re: [Spaceships] Designers' Championship I: ground to LEO
 

0.8? I wonder why. I think circular orbit velocity was equal to escape velocity on SQRT(2).

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Its true that its a long while since I did any orbital mechanics, and I don't fancy doing the integrals right now either. The questions I will ask are:

Where does the energy go? A rocket ends up with the same potential energy, regardless of 3G or 1.1G acceleration if it finishes in the same orbit. However, flying straight up at either thrust won't end you in a stable orbit, so this isn't necessarily straightforward.

GURPS Spaceships doesn't take any fuel-efficiency variations into account. Why not? That said, its a role-playing system designed for people who probably don't like integrals. Its probably simplified.

It sounds like it probably doesn't matter too much for the purposes of the contest. Which isn't the same as me claiming vindication.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

It isn't that hard to imagine a scenario where all the energy just goes "away" (heat probably) in the degenerate case of a say 0,1 G thrust rocket.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

1) goto to http://www.orbitersim.com download orbiter and launch some rockets to get a feel how it works.

2) Your orbit is the result of a vertical vector and a horizontal vector. At burnout you want your vertical vector to be ZERO and your horizontal vector to be orbital velocity. Your orbital velocity is dependent on high your orbit is.

The problem is that you need to go vertically to that high in the first place. But at the end you need to be going horizontally.

If you have unlimited fuel you could go up to the desired height, start thrusting horizontal thrust while maintaining enough vertical thrust so you don't fall until you reach orbital velocity.

If you don't then that where trajectory analysis comes in. Your trajectory will start straight up and gradually pitch down until you are horizontal at some point. The idea is to gain height and horizontal velocity while minimizing the loss of velocity in your vertical component due to gravity.

Basically the first part of your trajectory is design to gain enough vertical velocity so that the second half of your trajectory can be designed to gain horizontal velocity. At the end of your trajectory your vertical velocity will be zero.

This all assume you are trying to reach a circular orbit. Other types of orbits have their own target altitude, horizontal, and vertical velocity. But the idea is the same. At the end of the trajectory your are the right height, with the right combination of horizontal and vertical velocity.

Last for Earth and other inhabitable planets, you have to account for drag induced by the atmosphere. Of particular important is dynamic pressures. There is a point, called MaxQ, where dynamic pressure is at a maximum during ascent. It can be great enough to tear your vessel apart. So a trajectory has to be designed to account for both atmospheric drag and keeping MaxQ within the vessel's structural limit.

Both atmospheric drag and gravity's pull on your vertical velocity are the reason why you want to have a high thrust in trying to get into orbit. The more time you spending getting up to speed the more time both drag and gravity have to bleed off your speed. This will raise the amount of delta-vee needed to get into orbit.

Finally for game purpose all of this can be abstracted away by a simple delta-vee formula. You will need slightly more delta-vee for a world with an atmosphere. If you want to get more complex you could factor in the thrust time. In this case the higher a planet's gravity the worse the effect on a low thrust engine. But I think the current rules are good enough for the purpose.

While I am not from NASA or the aerospace industry. I spent a number of years developing add-ons for orbiter that accurate replicate the performance and controls of the Mercury and Gemini space capsule. This included the rockets they rode on (Redstone, Atlas-D, Titan 2).

Orbiter has a text configuration option for spacecraft. you can go in and change the parameters to whatever design you come up with. Fly it on the trajectory you will think works and find out what really happens.

Enjoy
Rob Conley
http://www.ibilbio.org

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Thanks for taking a look!

You won't be injecting antimatter until you are at high altitude. I'm not sure what the radiation effects from a few micrograms of antimatter will be at sea level.

The antimatter thermal rocket uses antimatter catalyzed hydrogen, at 1.8 mps per tank. Per pg 46, AMC hydrogen costs $20,000 per ton. With 1.5 tons per tank, fuel cost is: (20k$/t * 1.5t/tank * 1 tank/1.8mps) or $16,667 per mps.

I think you may have overcosted your operational insurance servicing costs on the Alida. It looks like you used 1% of the total ship cost for servicing, when Post 1 indicates 0.01% (1/10000) of the engine+tank cost. Operational insurance should be 0.01% of your total ship cost, assuming a 10x multiple for handling. This should bring your cost down slightly.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Most of it goes into the exhaust.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Oops. I looked straight past that and saw the the AM boosted stuff. I must learn to always read the small print ;-)

That should make your design pretty cost effective.

Hmm, so it should, again I misread it to be what I was expecting to see rather than what it said. Those numbers are truly tiny (and unlikely, I think they are mis-typed).

Why x10 for handling? It is winged so handling is 4. Did I miss some more small print?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Did you really mean to say one thousandth of 1 percent for operational insurance per trip? and one-hundredth of 1 percent for servicing? It seems way too low.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I'm not sure if the handling modifier was for space or atmosphere.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I don't think you can get a Hnd of 4 without wings, even with a 1000G of thrust :-0

Re: [Spaceships] Designers' Championship I: ground to LEO
 

According to Chansith's formula I calculate

1.2G is 55% fuel efficient (8.3 mps dV required)
1.5G is 75% (6.2)
2.0G is 87% (5.3)
2.5G is 92% (5.0)
3.0G is 94% (4.9)

So I could drop the thrust (and engines) of the Alida to 2G to make it only 87% efficient as long as I have at least 5.3 mps of deltaV (which I already do). It works out much more economical as I get another 3 passengers to share the cost.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

TL9+ Orbital Lighter (Spaceplane) v3 "Alida"

Alida class space planes are cheap reusable single stage orbital lighters that can take off and land at a normal airport anywhere in the world. The relatively low 2G drive allows for a reasonably comfortable passenger experience. It can easily make the return journey to and from orbit once for every two orbits of the space station or every 180 minutes.

Using Nuclear Thermal Rockets in fuel-less air-ram mode to take off it clears local population centres before going supersonic and accelerating to maximum air speed in an easterly direction. It then engages the other normal Nuclear Thermal rockets and climbs into orbit in seven minutes. Having docked and exchanged passengers it re-enters atmosphere and then makes a rapid descent back to Earth. Again using its air-ram engines it lands at an airport.

Its reserve delta-V allows for the Alida to enter orbit from higher latitudes rather than on the equator (e.g. Europe) and hence not have the full benefit of 0.25 mps from equatorial spin. It also allows it to enter orbit even if one of the engines fails during boost. Normally it enters orbit with at least two tons of hydrogen remaining which it can sell in orbit at a profit.

Front
1 Armor (Advanced Laminate)
2-6 Passenger Seating (10 seats)
0 Control Room

Central
1-0 Fuel Tank (Hydrogen)

Rear
1-2 Fuel Tank (Hydrogen)
3-4 Nuclear Thermal Rocket (1.0G)
5-6 Nuclear Thermal Ram-Rocket (1.0G)

dST/dHP 20, Hnd 4 atmo/0 space, SR 4/5, HT 12, Move Flight 1G/2500 mph/0.69 mps, Move Boost 2G/5.67 mps, LWt 30, Load 1.1, SM +5, Occ 1+10 SV, dDR 3, Cost M$ 2.21, TL9, Streamlined, Winged, Length 15 yards

DeltaV 6.36 mps (1+ mps reserve)
-Ram Rocket 2500mph = 0.69 mps
-9 Hydrogen Fuel Tanks = 9*0.45*1.4 (9 tank adjustment) = 5.67 mps

Note losses due to gravity drag of the 2G drive means that the boost phase is only 87% efficient in fuel usage, and so requires a total of 5.2 mps delta-V to reach orbit ([4.6-0.69]/0.87 + 0.69). The fuel reserve of over 1 mps allows the Alida to make orbit even if one of its four engines fail (and efficiency drops to 75%).

Economics:

1 flight every 3 hours operating for 7200 hours pa= 2400 flights per year
10 passenger seats at 75% loading = 7.5 passengers per trip
= 18,000 passengers per year

Variable cost per trip:
Insurance = M$2.21 * 0.001% = $22
Servicing = M$2.04 * 0.01% = $204
Fuel: 13.5 tons Hydrogen (K$27)

Total Variable Cost = K$ 27.226

Annual Costs to Amortise:
Requires 4 pilots at $7200 pm TL9 Comfortable salary each = K$345.6 pa
Other economics = Insurance + Depreciation + RoI = 10% = K$ 221

Total Fixed Cost = K$ 566.6

Divided over 2400 trips = $236 per trip

Return Ticket price = K$27.5 / 7.5 passengers = $3,700 (1 months income for an average TL9 job)

Note this price assumes the excess hydrogen fuel is wasted and not sold on or reused. So there is scope to reduce the price further to around $3000 per passenger.

There is no significant difference between TLs. The pilots wages do increase per TL, but this only adds about $30 per TL to the ticket price.

On a backwoods world with only 10% of the demand you only employ one pilot part time so annual costs are K$34.56 + K$221 = K$256 / 240 trips = $1065 per trip

So ticket price per passenger increases by $142 to $3,850 on backwoods worlds

The ticket price should stay approximately the same as ship size increases.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

That looks good. Why just two ram-rockets out of 4?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I was thinking cost and maintenance cost.

Though you have a good point, extra fuel-less delta-V saves Hydrogen fuel on every flight. The extra 0.28mps pre boost would save 0.76 tons of fuel per trip or $1520 * 2400 trips = K$3600 per year. Wow.

Yup, it needs 4 ram-rockets.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

If you don't mind the extra G's in atmosphere, what about an additional high-thrust ram-rocket, only used in atmosphere? That should save you ~0.22 mps worth of fuel per trip.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I am not sure there is one? There isn't an HT option listed under Fission rockets. There is one under AM NTR rockets, but I don't think I can use that.

I am looking for a way to use water as reaction mass, because then I can go down to 1 passenger per trip and it is still more economical. As long as I can fit the drives and fuel in 17 spaces it is doable.

Hmm, 15 fuel tanks (water) plus 2 water NTR ram-rockets is tantalisingly close to doable. ... I have an idea about burning some fuel to get air speed rather than orbit, but I need to do the math.

How long does it take to get air speed from 2500 mph to 4300 mph at 3G? I think it is 30 seconds, which is almost 4 tanks of fuel.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

OK I can't make it work with just water, yet... But I can make it work with one water NTR and one hydrogen NTR, a quarter of the fuel is hydrogen.

Edit: Not sure if that helps the ticket price much.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Using two different drives: half water, half hydrogen I reduced the return ticket price to low-earth-orbit to $2,400.

If we can work out how to do an all water drive the ticket price should drop to about half this.

TL9+ Orbital Lighter (Spaceplane) v5 "Alida"

Alida class space planes are cheap reusable single stage orbital lighters that can take off and land at a normal airport anywhere in the world. The relatively low 2G drive allows for a reasonably comfortable passenger experience. It can easily make the return journey to and from orbit once for every two orbits of the space station or every 180 minutes.

Using Nuclear Thermal Rockets in fuel-less air-ram mode to take off it clears local population centres before going supersonic and accelerating to maximum air speed in an easterly direction. It then boosts into orbit in less than seven minutes. Having docked and exchanged passengers it re-enters atmosphere and then makes a rapid descent back to Earth. Again using its air-ram engines it lands at an airport.

A novelty of the design is it uses two different fuels to reach orbit in order to reduce both the craft price and running costs. Half of its fuel delta-V comes from Hydrogen and half from Water.

Front
1 Armor (Advanced Laminate)
2-3 Passenger Seating (6 seats)
5-6 Fuel Tank (Water)
0 Control Room

Central
1-0 Fuel Tank (Water)

Rear
1 Fuel Tank (0.75 Water, 0.25 Hydrogen)
2-4 Fuel Tank (Hydrogen)
5 Nuclear Thermal Ram-Rocket (Hydrogen 0.5G)
6 Nuclear Thermal Ram-Rocket (Water 1.5G)

dST/dHP 20, Hnd 4 atmo/0 space, SR 4/5, HT 12, Move Flight 1G/2500 mph/0.69 mps, Move Boost 2G/4.68 mps, LWt 30, Load 0.7, SM +5, Occ 1+6 SV, dDR 3, Cost M$ 1.93, TL9, Streamlined, Winged, Length 15 yards

DeltaV 5.37 mps (0.17 mps reserve)
-Ram Rocket 2500mph = 0.69 mps
-9.75 Water Fuel Tanks 9.75*.15*1.6 (13 tank adjustment) = 2.34 mps
-3.25 Hydrogen Fuel Tanks = 3.25*0.45*1.6 (13 tank adjustment) = 2.34 mps

Note losses due to gravity drag of a 2G drive means that the boost phase is only 87% efficient in fuel usage, and so requires a total of 5.2 mps delta-V to reach orbit ([4.6-0.69]/0.87 + 0.69).

Economics:

1 flight every 3 hours operating for 7200 hours pa= 2400 flights per year
6 passenger seats at 75% loading = 4.5 passengers per trip
= 10,800 passengers per year

Variable cost per trip:
Insurance = M$1.93 * 0.001% = $19
Servicing = M$1.78 * 0.01% = $178
Fuel: 4.875 tons Hydrogen = $9,750
Fuel: 10.75 tons Water = $293

Total Variable Cost = $ 10,240

Annual Costs to Amortise:
Requires 4 pilots at $7200 pm TL9 Comfortable salary each = K$228 pa
Other economics = Insurance + Depreciation + RoI = 10% = K$ 193

Total Fixed Cost = K$ 538.6

Divided over 2400 trips = $224 per trip

Return Ticket price = $10,465 / 4.5 passengers = $2,325 (less than 3 weeks income for an average TL9 job)

There is no significant difference between TLs. The pilots wages increase per TL, which adds only about $30 per TL to the ticket price.

On a backwoods world with only 10% of the demand you only employ one pilot part time so annual costs are K$34.56 + K$193 = K$376 / 240 trips = $950 per trip. So ticket price per passenger increases by $210 to $2,535 on backwoods worlds

The ticket price should stay approximately the same as ship size increases.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

This is a bit of a cheat, but note that using water increased thrust and therefore increases airspeed, and that this works even when you are in air-ram mode, and not using your fuel--so the lost of delta-v doesn't matter much.

Actually, that isn't terribly unrealistic: air has an average molecular weight of about 29, and therefore really ought to give you 3.8 times the thrust of hydogen. It isn't RAW or groundrules, but realistically a winged design with four NTR ram-rockets can get up to about 2 miles per second without using any fuel at all. (Thrust is nearly 8 gee, but balanced by air resistance: it won't squash the passengers). Six tanks of hydrogen will get you up to 4.7 miles per second, plus 0.25 from rotation gets you into orbit. The craft is a bit pricey, but allows 14 spaces of passenger seating.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I like the progressive refinement that's been done to the Alida craft. Maybe we'll meet in orbit 20 years hence after riding a very similar spacecraft. However, I've had a few thoughts regarding the design. If you want to save the eye-strain, the first three are annoying commentary. The last one is potentially useful.

1)
From what I've read, it seems that the biggest issue doesn't come from radioactive exhaust (unless you directly pass air into the reactor instead of using exchangers) but directly from the reactor itself. Reactors would tend to require a lot of shielding to protect pilots, which is why some historical nuclear aircraft (ram or otherwise) were unmanned concepts. All that being said, it's possible that a TL9 reactor could be build efficiently enough that radioactivity and required shielding is minimized.

2)
Now, another issue that needs to be contended with in a nuclear aircraft is the potential for failure. Would the aircraft have failure modes to ensure that the nuclear reactors wouldn't pose a threat of contamination? It's possible to launch the aircraft over oceans, but there is always the possibility of the aircraft failing over land and the possibility that failure over an ocean could still lead to radioactivity being carried to a population center through ocean currents or causing problems with marine life. Again, here's a situation we could handwave away by saying that a TL9 reactor would be using safer power generation methods, maybe some variant of a pebble-bed, which would also help with refueling, but failure is still a potential problem. If a nuclear lighter such as this design is ever proposed, expect anti-nuke protests.

3)
Nuclear issues aside, I've had a couple of other thoughts specifically about the design. One issue is that the water rocket will burn out faster than the hydrogen rocket - they both provide the same amount of dV, but the water rocket produces 3x the thrust and will therefore burn out 3x as fast. You could assume that the pilot varies the level of water being fired in order to maximize ascent characteristics, or you could even assume that both rockets are capable of firing hydrogen or water and able to vary the mix since they are already capable of variable fluid-flow due to being ram-rockets. Of course, I'm not sure what the overall effect would be on your dV requirements, making this paragraph more of a nuisance than anything else...

4)
Now the only thought of mine that you can actually easily apply to the craft is to assume that the craft doesn't have a physical pilot. Alida could potentially be flown by computer, especially since the flight path would be set before-hand. This would allow for one more passenger seat where the controls used to be and eliminate the expense of a pilot, though it would add the expense of better computing and AI flight software.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

I thought about it and decided it was being cheesy. However if being cheesy actually makes it more realistic then perhaps I will rethink.

If I could get the average per engine air-thrust to 1G for each of two engines then an all water design is doable.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

See you in LEO, 12th January 2028 ;-) Unfortunately I don't think the Alida is early TL9. Maybe 40 years?

Check. Anti rad nano are Transhuman Space tech. Though not sure about the core Gurps TL for that.

Check. But it's either nuclear drive or global warming drive - take your pick ;-)

Fission air-rams are a no-global-warming alternative for jet engines too. So if we can make them relatively safe then we can save all our flight carbon emissions.

I thought I had that covered by having 3 times the fuel tank? Edit: The water rocket takes the same amount of time to burn the same deltaV.

And AI is the same Gurps TL as the craft (TL9).

Or AI pilot with remote living pilot on standby (remotely piloted space shuttle).

Actually I can make an all water craft work (with 0.66 mps excess) if I just have one passenger in the pilot seat (16 tank, 2 drive, armor, controls). The return ticket price for that one passenger (actually 0.75 passenger by the ground rules) would be only $1200 assuming I have to pay the AI pilot (or $1000 if I don't).

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Edit: updated for two orbiters, associated economics, and extra color text.

I found a way to use an all water design and get the ticket price below 1 weeks wages...

TL9+ Orbital Lighter (Lifter and Spaceplane) v6 "Alida"

Alida class space planes are cheap reusable two part orbital lighters that can take off and land at a normal landing strip anywhere in the world that has a clean water supply. It can easily make the return journey to and from orbit once for every two orbits of the space station or every 180 minutes.

The lifter craft and the orbiter craft are both capable of independent operation and flight. The orbiter rides under the lifter until separation above the atmosphere. Both use easy to obtain water as their reaction mass.

Using Nuclear Thermal Rockets in fuel-less air-ram mode the lifter takes off and clears local population centers before going supersonic and accelerating to maximum air speed in an easterly direction. It then boosts towards orbit until it runs out of reaction mass. At this point the orbiter detaches and engages its rockets and completes the climb into orbit. The lifter drops back into atmosphere and flies back to its base using its engines in air-ram mode.

Having docked and exchanged passengers the orbiter re-enters atmosphere and then makes a rapid descent back to Earth. Again using its air-ram engines it lands on its airstrip about an hour after it took off. There it picks up a second Alida orbiter and makes the trip again half an hour later. The Lifter therefore cycles every 90 minutes and each orbiter every 180 minutes.

Typically these craft take off over water and international airspace as few countries want fission craft flying over their territory. So, they typically take off from equatorial coastal countries and islands with several hundred miles of water to their east.

Alida Lifter “Big Al”:

Front
1-6 Upper Stage (Orbiter)

Central
1 Armor (Metallic Laminate)
2-6 Fuel Tank (Water)
0 Control Room

Rear
1-2 Nuclear Thermal Ram-Rocket (Water 3G)
3-0 Fuel Tank (Water)

dST/dHP 30, Hnd 4 atmo/0 space, SR 5/4, HT 12, Move Flight 1G/2500 mph/0.69 mps, Move Boost 3G/2.1 mps, LWt 100, Load 0.1, SM +6, Occ 2+0 SV, dDR 3, Cost M$ 6.1, TL9, Streamlined, Winged, Length 40 yards

DeltaV 2.79 mps (effective 2.67 mps after gravity drag)
-Ram Rocket 2500mph = 0.69 mps
-10 Water Fuel Tanks 10*0.15*1.4 (10 tank adjustment) = 2.1 mps

Alida Orbiters “Little One” and “Little Two”:

Front
1 Armor (Metallic Laminate)
2-0 Passenger Seating (12 seats)

Central
1-6 Fuel Tank (Water)
0 Control Room

Rear
1-4 Fuel Tank (Water)
5-6 Nuclear Thermal Ram-Rocket (Water 3G)

dST/dHP 20, Hnd 4 atmo/0 space, SR 5/4, HT 12, Move Flight 1G/2500 mph/0.69 mps, Move Boost 3G/2.1 mps, LWt 30, Load 1.3, SM +5, Occ 1+12 SV, dDR 2, Cost M$ 1.9, TL9, Streamlined, Winged, Length 20 yards

DeltaV 2.1 mps (effective 1.98 mps after gravity drag)
-10 Water Fuel Tanks 10*0.15*1.4 (10 tank adjustment) = 2.1 mps

Combined Effective Delta-V of Lifter and Spaceplane = 2.67 + 1.98 = 4.65 mps

Economics:

1 flight every 3 hours operating for 7200 hours pa= 2400 flights per year
12 passenger seats at 75% loading = 9 passengers per trip
= 21,600 passengers per year per orbiter
= 43,200 for two orbiters

Variable cost per orbiter trip (includes use of lifter):
Insurance = M$8.0 * 0.001% = $99
Servicing = M$6.9* 0.01% = $690
Fuel: 65 tons Water (50+15) = $1300

Total Variable Cost = $ 2,089

Annual Costs to Amortise from two orbiters and one lifter:
Requires 12 pilots at $7200 pm TL9 Comfortable salary each = K$1,037 pa
Other economics = Insurance + Depreciation + RoI = 10% = K$990

Total Fixed Cost = K$ 2,027

Divided over 4800 trips = $423 per trip

Return Ticket price = $(2089+423) / 9 passengers = $279 (less than 1 weeks net income for an average TL9 job)

There is no significant difference between TLs. The pilots wages increase per TL, which adds only about $10 per TL to the ticket price.

On a backwoods world with only 10% of the demand you only employ two pilots part time and only have one orbiter so annual costs are K$70 + K$800 = K$870 / 480 trips = $1813 per trip. So ticket price per passenger increases to $434 on backwoods worlds

The ticket price should stay approximately the same as ship size increases if you want to scale up to bigger craft and more passengers per trip.

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Excellent! Can you use one lifter to juggle two or even three orbiters?

Re: [Spaceships] Designers' Championship I: ground to LEO
 

Given the fixed space station orbital period probably just two. It only saves about $30 per ticket though.