[Space, Spaceships] Mars Semi-Cycler?

[DaltonS]

I've been studying the idea of the Mars Cycler, and I have to say that it's a lot more complicated that it looks at first glance. Part of it is the orbital mechanics and the rest of it is the logistics. While the cycler itself would use much less ∆V that other Mars mission profiles, it's more than made up for by the "taxi" craft that shuttle passengers to and from the cycler during flybys . (Since the "taxis" would be much smaller than cycler, the absolute amount of propellant expended would be less.) Still, the idea of traveling on an interplanetary "Flying Dutchman" is a bit daunting.

I've come to prefer the idea of the free-return semi-cycler. Instead of using an orbit based on the Earth-Mars synodic period (780 days), the ship would use a free-return orbit of exactly 2 years (730.5 days) which would require two 3.16 mps burns to leave and re-enter Earth orbit, where it stay for 49.5 days being refueled and refurbished for the next mission. According to my calculations, the taxis would require a ∆V of 5.68 mps between the cycler and Mars orbit each way because the transfer orbit crosses that of Mars at an angle of 21.6 degrees. Below is my example of a TL9 cycler.

Perdue-Class Medium Interplanetary Transport

PILOTING/TL9 (LOW-PERFORMANCE SPACECRAFT)

TL  Spacecraft  dST/dHP  Hnd/SR  HT       Move        LWt.     Load    SM      Occ      dDR  Range    Cost   
 9    Perdue       70     -4/5   13  0.0002G/10 mps  1,000  396.4 [1]  +8  10ASV [2,3]   10    —    $18.74M

Length: 50 yd. (150 ft.) Crush Depth: 30.3 Atmospheres (1,000 ft.)
Power Points: +1 / -1
Space Performance: sAccel: 0.0002Gs/10 mps


SHIP SYSTEMS

 FRONT  
[1]     Armor - Metallic Laminate
          dDR 10
[2-3]   Cargo Hold
          100 Tons / SM+3 Bay Doors
[4-6]   Hangar Bay
          Cap.: 90 Tons / SM+5 / Launch: 50 Tons/min
[Core]  Control Room
          Computer: C6 / Comm/Sensor: 6 / 4 Stations

CENTER  
[1]     Armor - Metallic Laminate
          dDR 10
[2]     External Clamp
          1,000 Tons
[3-6]   Vehicle Dock
          200 Ton Capacity / SM+0 [4]
[Core]  Habitat
          6 Cabins

 REAR   
[1]     Armor - Metallic Laminate
          dDR 10
[2†]    Power Plant - Fission Reactor
          1 Power Point / 50 yr Fuel [5]
[3!]    Reaction Engine - VASIMR Electric Rocket
          0.0002Gs / 10 mps / 0.002Gs / 0.5 mps / 95 days Fuel [6,7]
[4]     Engine Room
          1 Workspace
[5]     Fuel Tank
          50 Tons of Hydrogen
[6]     Habitat
          6 Cabins

User Notes: The modular Vehicle Docks can hold two SM+6 auxiliary craft, usually atmospheric craft such as Midnight-Sun or Condor class shuttles used as orbital taxis. (Modularity allows the customized docks to be swapped in and out as required.)
Design Switches, Features, & Notes: 4 Airlocks (Capacity: 4 people each), Refueling Cost: $100,000, Food Supplies: $15,000
[1] Load includes: 1.4*tons of Crew & Passengers, 15*tons of Standard Food (7,500*man-days / 750*days), 90*tons of Cargo Hold, 200*tons of Vehicle Dock, 90*tons of Hangar Bay
[2] Plus 4 in Hibernation Chambers, [3] Crew Requirement (9 total): 4 Control Stations (1 Captain/Pilot, 1 Operations
Officer, 1 Chief Engineering, 1 Navigator/Comm/Sensor Operator), 1 Technician, 2 Entertainment, 2 Lab Workers
[4] Modular
FUEL USED: [5] Fissionables, [6] Hydrogen (50 tons)
PERFORMANCE PROFILES: [7] Space Profile #1


AUXILIARY CRAFT

Qty.                   Ship                     Cost         Mass  
   1  Sling Liner Passenger Barge                  $216k       30
   1  Kobold Work Bug                          $1.12515M       30
   1  Aurora Orbital Transfer Vehicle (OTV)      $811.6k       30

HABITATS

Qty.   Location             Type           SM         Notes         
   3  Center [C]  Cabin                    +0             6 person
   1  Center [C]  Bunkroom                 +0             4 person
   1  Center [C]  Establishment: Rec Room  +0  20 patrons, 2 staff
   1   Rear [6]   Lab: Standard            +0   2 person, +1 Skill
   4   Rear [6]   Hibernation Chamber      +0           4 chambers
   1   Rear [6]   Sickbay                  +0      1 bed; +2 Skill
   1   Rear [6]   Minifac: Fabricator      +0         $500 per Hr.
   1   Rear [6]   Steerage Cargo           +0               5 tons

Created using GURPS Spaceship Design Spreadsheet v2.0 RC 7. GURPS Spaceships Design Spreadsheet is copyright © 2009-2013 Eric B. Smith. This spreadsheet is based on information contained in the GURPS Spaceships series of books.

Dalton "like/dislike/discuss?" Spence

[RogerBW]

Originally Posted by DaltonS

I've been studying the idea of the Mars Cycler, and I have to say that it's a lot more complicated that it looks at first glance. Part of it is the orbital mechanics and the rest of it is the logistics.

The only saving you get by using a cycler setup is in the delta-V for the mass of stuff that doesn't have to leave the cycler: fixed life support plant, radiation shielding, and so on. Depending on the genre assumptions that may be important or trivial.

[Fred Brackin]

Why are you assessing Delta-V of differently sized vehicles against each other?

It's that total mass of propellant that's the proper measuring stick and you admit it would be less for a cycler.

[Stripe]

Awesome write up!

[vierasmarius]

Another option would be to snag a passing asteroid and nudge it into an appropriate orbit with mass drivers. As a plus, the mass of rock can serve as basic radiation shielding.

[RogerBW]

Originally Posted by Fred Brackin

Why are you assessing Delta-V of differently sized vehicles against each other?

It's that total mass of propellant that's the proper measuring stick and you admit it would be less for a cycler.

Only if the bits that aren't needed at either end are significantly massive. Which is true in some scenarios but not in all. I'm not objecting to the concept, just noting that you need to make some tech assumptions to make it work.

[thrash]

Originally Posted by vierasmarius

Another option would be to snag a passing asteroid and nudge it into an appropriate orbit with mass drivers. As a plus, the mass of rock can serve as basic radiation shielding.

You'd need multiple asteroids to cover the phase differences (that is, if you want to travel more than once every 15 years). If you choose the right rock, or the right thrusters for your shuttles, you might be able to refuel from the rock. This would more than double the amount of payload the shuttles can carry, or more than halve their size.

Setting up small (~150) colonies on the cycler asteroids would be an intermediate step between colonizing the Martian moons and reaching out into the Main Belt. Sure, it's isolated most of the time, but every couple of years you make a pass by Earth or Mars. You have a ready market for all the food you've grown and stockpiled in the interval in the hordes of colonists who briefly fill your otherwise empty barracks (or hotels, for the well-heeled). You trade food, lodging, and reaction mass for a share of the high-tech goods that are passing through. It actually makes better economic sense than most asteroid colony schemes.

[Fred Brackin]

Originally Posted by RogerBW

Only if the bits that aren't needed at either end are significantly massive. Which is true in some scenarios but not in all. I'm not objecting to the concept, just noting that you need to make some tech assumptions to make it work.

I was addressing the OP and his concerns.

[DaltonS]

Here is an enlarged version of the Perdue-class Semi-Cycler.

PERDUE (PERDUE-CLASS MEDIUM INTERPLANETARY TRANSPORT)
PILOTING/TL9 (LOW-PERFORMANCE SPACECRAFT) Page:

TL   Name   dST/dHP  Hnd/SR  HT       Move        LWt.      Load     SM      Occ      dDR  Range   Cost   
9^  Perdue    100     -5/4   13  0.0002G/20 mps  3,000  1,254.2 [1]  +9  34ASV [2,3]   15    —    $52.5M

Length: 70 yd. (210 ft.) Crush Depth: 32.5 Atmospheres (1,071 ft.)
Power Points: +1 / -1
Space Performance #1: sAccel: 0.0002Gs/20 mps
Space Performance #2: sAccel: 0.002Gs/1 mps

SHIP SYSTEMS

 FRONT   
[1]      Metallic Laminate Armor
           dDR 15
[2-4]    Hangar Bay
           Cap.: 300 Tons / SM+6 / Launch: 100 Tons/min
[5-6]    Cargo Hold
           300 Tons / SM+4 Bay Doors
[Core]   Smaller SM Systems
           SM+8
  [a]    Control Room
           Comp: C6 / Comm/Sensor: 6 / 4 Stations
  [b-c]  Habitat
           two bunkrooms, two cabins, one rec room
           eight hibernation chambers, one sickbay, one lab, one fabricator minifac

 CENTER  
[1]      Metallic Laminate Armor
           dDR 15
[2-3]    Vehicle Dock
           300 Ton Capacity / SM+7 [4]
[4]      External Clamp
           3,000 Tons
[5-6]    Vehicle Dock
           300 Ton Capacity / SM+7 [4]
[Core]   Habitat
           one bunkroom, nine passenger cabins, 50 tons of steerage cargo

  REAR   
[1]      Metallic Laminate Armor
           dDR 15
[2†]     Fission Reactor
           1 Power Point / 50 yr Fuel [5]
[3!]     VASIMR Electric Rocket
           0.0002 Gs / 20 mps / 0.002 Gs / 1 mps / 190 days Fuel [3,3,6]
[4]      Engine Room
           1 Control Station / 2 Workspaces
[5-6]    Fuel Tank
           300 Tons of Hydrogen

User Notes: The modular Vehicle Docks can hold two SM+7 (300-ton) auxiliary craft, usually atmospheric craft used as orbital taxis. (Modularity allows the customized docks to be swapped in and out as required.) If an auxiliary craft has habitat modules installed, the crew usually stays aboard their ship to stretch life support; otherwise they travel as passengers or in hibernation chambers.
Design Switches, Features, & Notes: 3 Airlocks (Capacity: 5 people each), Fuel Cost: $600,000; Auxiliary Craft Cost: $61,467,220; Standard Food Cost: $50,000; Total Cost: $114,617,220
CAMPAIGN OPTIONS: EBS's Unofficial rules
[1] Load includes: 4.2 tons of Crew & Passengers, 50 tons of Standard Food, (25,000 man-days / 735 days), 300 tons in Cargo Hold, 600 tons in Vehicle Dock capacity, 300 tons in Hangar Bay
[2] Plus 8 in Hibernation Chambers, [3] Crew Requirement (16 total): 4 Control Stations (1 Captain/Pilot, 1 Operations Officer, 1 Chief Engineer,
1 Navigator/Comm/Sensor Operator), 1 Technician, 5 Auxiliary Craft Crew, 2 Passenger Care, 1 Entertainment, 1 Medical, 2 Scientists
SYSTEM NOTES: [4] Modular
FUEL USED: [5] Fissionables, [6] Hydrogen (300 tons)

AUXILIARY CRAFT

Qty.                 Ship                 Location     Cost    Mass  Crew  
   1  Aurora-Class OTV                    Front     $811.6k    30    1
   1  Condor Spaceplane                   Front     $8.89M     100   2
   1  Kobold Work Bug                     Front     $1.12662M  30    2
   1  Midnight Sun-Class Orbital Shuttle  Front     $1.468M    100   2
   1  Rickenbacker Escape Pod             Front     $155k      10    0
   1  Sling Liner Passenger Barge         Front     $216k      30    1
   2  Mars Trans-Orbital Taxi             Center    $48.8M     600   4

HABITATS

Qty.   Location           Type          SM         Notes         
   2  Front [Cb]  Bunkrooms             +0             8 person
   2  Front [Cb]  Cabins                +0             4 person
   1  Front [Cb]  Rec Room              +0  20 patrons, 2 staff
   8  Front [Cc]  Hibernation Chambers  +0           8 chambers
   1  Front [Cc]  Sickbay               +0      1 bed; +2 Skill
   1  Front [Cc]  Lab                   +0   2 person, +1 Skill
   1  Front [Cc]  Fabricator Minifac    +0         $500 per Hr.
   1  Center [C]  Bunkroom              +0             4 person
   9  Center [C]  Passenger Cabins      +0            18 person
  10  Center [C]  Steerage Cargo        +0              50 tons

Created using the GURPS Spaceship Design Spreadsheet Version 2.0 RC 17 based on the GURPS Spaceships series of books. http://gurpsland.no-ip.org/#GURPSSpa...ignSpreadsheet

Please note that:

1. While this ship contains no superscience systems, it is listed as TL9^ because the Orbital Taxis it uses have a reconfigurable fission reactor/NTR ram-rocket to power its VASMIR drive and liftoff from Mars. (I'll post its design later.)
2. The control room remains the same size (SM+8 system) and the crew habitats have been moved from the center and rear hulls to the front hull core.
3. While the semi-cycler still launches in a 2-year free return trajectory for safety reasons, its doubled ∆V allows it to perform the Mars Orbit burn itself, so it can loiter in Mars orbit until the proper return window occurs.

Dalton “just call me an equine necromancer” Spence

[DaltonS]

Originally Posted by DaltonS

I've come to prefer the idea of the free-return semi-cycler. Instead of using an orbit based on the Earth-Mars synodic period (780 days), the ship would use a free-return orbit of exactly 2 years (730.5 days) which would require two 3.16 mps burns to leave and re-enter Earth orbit, where it stay for 49.5 days being refueled and refurbished for the next mission. According to my calculations, the taxis would require a ∆V of 5.68 mps between the cycler and Mars orbit each way because the transfer orbit crosses that of Mars at an angle of 21.6 degrees.

I've come to a bit of a quandary. According to my calculations based on these formulas, the time of flight from Earth to Mars orbit should be 127 days. However, according to GURPS Mars

With a delta-V of 3.2 miles per second (11,520 mph), the crew can follow a free-return path which will get them to Mars in 180 days; this speed is still low enough to make aerobraking at Mars practical.

Trajectories sidebar, p.32

That's almost 8 weeks difference. Have I missed something?

Dalton “who is proud of his "One-Tangent Burn" spreadsheet” Spence