Orbital Base Jumping

[Agemegos]

Originally Posted by vicky_molokh

So why not use the scheme similar to the one in Tiberian Sun?

Example build:

TL	Spacecraft		dST/dHP	Hnd/SR	HT	Move	LWt.	Load	SM	Occ	dDR	Range	Cost
10	Marine Drop Pod		15	0 / 4	12	3G/0.15	10	0.5	+4	10	3	$1.265M

Length: 10 yd. (30 ft.)   Crew Requirement: 1 [2]   Power Points: +4 / -5   Air Performance:  Speed: 4,300 mph / 3G / 0.15 mps   Hnd/SR: +4 / 4

[edit]Streamlined and winged, mostly for manoeuvre purposes.[/edit]

Systems:
Front:
1. Armor
2. Soft Landing System
3-6. Passenger Seating.

Central:
1. Armor.
2-6. Major Battery - Turret (with gunner each).
Core: Control Room

Rear:
1. Armor
2-4. Defensive ECM.
5. Engine (e.g. Chemical Rocket)
6. Fuel for said engine
Core: small Antimatter Reactor

The thing carries 10 marines (1 pilot, 5 gunners already shooting when the thing is in the air, and 4 sitting just in case), has Hnd+4 for those aerial dodges, and packs a high-G (but low-endurance) drive for emergencies, breaking, and course-corrections outside atmosphere.

It looks like a dud to me. It doesn't have enough delta-v to re-enter without aerobraking, and it doesn't have enough dDR to aerobrake. The weapons are going to be a useless waste of space during re-entry (you can't see to target through the plasma sheath), and the engine has a burn endurance of only 8 seconds, which is not enough loiter time to provide useful air support after aerobraking.

As for slipping in cold, passenger seating gives you life support for 24 hours only. And you only have delta-v to brake from 0.15 mi/sec., which gives you a maximum range of 13,000 miles.

[Diomedes]

Originally Posted by Brett

It looks like a dud to me. It doesn't have enough delta-v to re-enter without aerobraking, and it doesn't have enough dDR to aerobrake.

Did I miss somewhere in Spaceships that says how much armor you need to aerobrake? I don't remember anything beyond needing at least one armor system in the front section.

[Snoman314]

Originally Posted by Diomedes

Did I miss somewhere in Spaceships that says how much armor you need to aerobrake? I don't remember anything beyond needing at least one armor system in the front section.

I don't recall seeing rules for it anywhere, other than, as you say a minimum of one armor sytem in the front or center hull sections. But that is only the requirement for streamlined hulls, not explicitly for re-entry. (although that seems implied, as a streamlined hull is the only requirement I can find for surviving entering an atmosphere at orbital velocities)
I'd also point out that the soft landing system explicitly includes a single use heat shield.

[Allu]

Originally Posted by Brett

It doesn't have enough delta-v to re-enter without aerobraking, and it doesn't have enough dDR to aerobrake.

Read the description of the Soft-Landing System again.

Edit: Ninja'd by the snowman.

[Agemegos]

Originally Posted by Diomedes

Did I miss somewhere in Spaceships that says how much armor you need to aerobrake?

Not as far as I am aware. As far as I know the only mention of aerobraking capacity is in the description of the soft-landing system. I have always presumed that real spaceships engine brake.

I base the DR100 criterion on the life pods and re-entry capsules in Ultra-Tech.

I don't remember anything beyond needing at least one armor system in the front section.

That's a requirement for being streamlined. "A streamlined spacecraft must be given at least one armour system on its front or central hull" (Spacehips p.10).

There is a box on p.40 (headed "atmospheric flight") that says that any streamlined and winged spacecraft can glide in to a landing without power. I guess you could take that as including braking, but I don't. Since the same box allows a powered landing with an expenditure of delta-v way less than orbital velocity I think I am on firm ground assuming that that box is about landing after any necessary braking.

[Agemegos]

Originally Posted by Allu

Read the description of the Soft-Landing System again.

Fair point. It can re-enter by aerobraking, but it still has a loiter time of only eight seconds, so I still think it's a dud.

[Diomedes]

Originally Posted by Brett

That's a requirement for being streamlined. "A streamlined spacecraft must be given at least one armour system on its front or central hull" (Spacehips p.10).

I tend to interpret that as meaning it needs the armor while doing something that only streamlined craft can do, which would mean either going ten times as fast in atmosphere, or aerobraking.

[Agemegos]

Originally Posted by Diomedes

I tend to interpret that as meaning it needs the armor while doing something that only streamlined craft can do, which would mean either going ten times as fast in atmosphere, or aerobraking.

I don't think it is either RAW or reasonable that streamlined vehicles can aerobrake without a heat shield. I'm prepared to be corrected about RAW, but as for reasonable it seems pretty clear that the kind of streamlining you use for going faster under power is the opposite of the blunt-front designs optimised for aerobraking.

[Snoman314]

Brett: You do realise that with sufficiently precise guidance, its possible to glide in after an aerobrake maneuver lasting many orbits, with very low peak heat load, low enough that passive cooling would be sufficient. Basically it requires crossing skip-reentry with aerobraking. Aerodynamic lift is used to hold the craft at a constant dynamic pressure, with constantly decreasing velocity and altitude.
Thats the idea anyway. In practice, there is plenty of opportunity to mess up the glide by going too high or low.
But I put it to you that DR100+ is not necessarily a requirement for re-entry. That the higher the DR/heat shielding, the easier and faster aerobraking is, but that it is not impossible for less well shielded craft.

The box on pg 40 has been discussed in the past, and if I remember correctly, the consensus was that 0.1mps was for each landing attempt after the approach to the ground had already been completed. I know that's not what it says, but its the only possible way it makes sense otherwise. Some have said this should be errata'd, but nothing seems to have been done that I've seen.
The fact that the passage on vertical landings mentions that streamlined craft can land quicker, to my mind supports the idea that streamlined craft are able to aerobrake/re-enter, otherwise how else is the extra deceleration accounted for?

I don't think it is either RAW or reasonable that streamlined vehicles can aerobrake without a heat shield. I'm prepared to be corrected about RAW, but as for reasonable it seems pretty clear that the kind of streamlining you use for going faster under power is the opposite of the blunt-front designs optimised for aerobraking.

Streamlined: A streamlined hull’s shape may be a wedge,
lifting body, cone, disk, teardrop, bullet, or needle-like shape. It
is optimized for high atmospheric speed.

Streamlined hulls do appear to explicitly include shapes suitable for aerobraking.

Finally please don't take my rebuttal personally Brett, I'm mainly just trying to keep the magic alive :).

[Allu]

Originally Posted by Brett

Fair point. It can re-enter by aerobraking, but it still has a loiter time of only eight seconds, so I still think it's a dud.

I'm more then willing to concede that a loiter time of eight seconds isn't really useful (though I'd allow a 24 second burn at 1G). The problem is that there isn't really any way around that problem (with a SM+4 craft). If you know you're only going to be dropping it on planets with atmospheric oxygen then you can exchange the chemical rocket for a jet engine but that means they can't get to the atmosphere on their own power (which might or might not be a problem).

A better solution is probably going to be something along the lines of the drop ships in SS4.