Questions about a Manned Mars vehicle

[Sarge00Seven]

Hello guys, this is my first post and I'm sorry if this is misplaced, but I have been developing a Manned spacecraft for a dual Venus/Mars Flyby. However I've hit a few roadblocks and hoping that some people in this forum would be capable of helping me. I have no idea how to calculate the amount of RCS fuel that I would need for the spacecraft for such a long mission (almost 600 days). Can anyone help me on how I could calculate it? I'm familiar with using delta V and Isp to figure out the amount of fuel I would need, but I'm totally at a loss for this. Also if anyone has any ideas on what experiments could be done on a manned deep space habitat, please feel free to post them. Thank you guys and I hope that this isn't misplaced.

[DBowman]

You'd have to model your craft mass distribution, RCS locations, RCS engine/propellant, craft attitude requirements (e.g. fixed solar arrays vs tracking arrays make different attitude maintenance demands), & maneuver plans. If your craft is large and has to maintain attitude even the solar wind is significant. I've got a link to a 60's Venus Mars flyby using Apollo derived hardware in this post (CSM + SkylabLite) they estimated a 0.5 gm solar wind force that had to be counteracted to maintain attitude - a few hundred pounds of RCS fuel (used to de-saturate flywheels). If you can find detailed mission plans for similar trajectories and craft you could use their numbers as a 'first cut'/guesstimate.

What kind of craft and crew are you thinking of?

[DerekL1963]

5 hours ago, Sarge00Seven said:

I have no idea how to calculate the amount of RCS fuel that I would need for the spacecraft for such a long mission (almost 600 days).

You can't calculate it, not directly anyhow.    You need to work through your reference mission plan, measuring the RCS fuel required at each step, and then sum up those amounts and add in a bit for reserves.   If the results are significantly different from those you used to generate your mission plan, you need to rework your weights and mission plan and start over again.  Spacecraft design (even at the theoretical level) is an iterative process.

This is one of the reasons why NASA has spent such effort coming up with reference mission designs for Mars missions - they're the foundation that underlies everything else.  The other reason is that it's cheap and makes them look busy.   An awful lot of NASA studies and "planning" are conducted for this reason - and who knows, maybe they'll get funded.

[Sarge00Seven]

Currently I have developed a craft with a 3 launch stack with 4 modules including from back to front  a cryogenic RP-1/LOX first stage to begin the Trans-Venus injection burn, a service module with a hypergolic fuel supply which also housed the majority of the electrical system, an inflatable habitation module based on Bigelow Aerospace's Sundancer, and finally a Dragon V2 for the Earth Return Vehicle. This is designed to support 2 people for a 590 day trajectory that was produced by JPL, utilizing a rocket assisted gravity slingshot around both Venus and Mars and then finally back to Earth. In addition, I was thinking that the craft itself should always need to keep its engine facing the sun so that a water layer could be kept between the astronauts and the solar radiation without needing to completely surround the ship. I'm working on a CAD model that I can post when it's done. Thanks for the feedback guys.

Edited February 12, 2016 by Sarge00Seven

[Sarge00Seven]

1 hour ago, DerekL1963 said:

You need to work through your reference mission plan, measuring the RCS fuel required at each step, and then sum up those amounts and add in a bit for reserves.

How would you measure this?

[DerekL1963]

Read DBowman's post above - you need a model of your RCS system and it's performance.

[fredinno]

On February 11, 2016 at 9:26 AM, Sarge00Seven said:

Hello guys, this is my first post and I'm sorry if this is misplaced, but I have been developing a Manned spacecraft for a dual Venus/Mars Flyby. However I've hit a few roadblocks and hoping that some people in this forum would be capable of helping me. I have no idea how to calculate the amount of RCS fuel that I would need for the spacecraft for such a long mission (almost 600 days). Can anyone help me on how I could calculate it? I'm familiar with using delta V and Isp to figure out the amount of fuel I would need, but I'm totally at a loss for this. Also if anyone has any ideas on what experiments could be done on a manned deep space habitat, please feel free to post them. Thank you guys and I hope that this isn't misplaced.

Use KSP 

18 hours ago, Sarge00Seven said:

Currently I have developed a craft with a 3 launch stack with 4 modules including from back to front  a cryogenic RP-1/LOX first stage to begin the Trans-Venus injection burn, a service module with a hypergolic fuel supply which also housed the majority of the electrical system, an inflatable habitation module based on Bigelow Aerospace's Sundancer, and finally a Dragon V2 for the Earth Return Vehicle. This is designed to support 2 people for a 590 day trajectory that was produced by JPL, utilizing a rocket assisted gravity slingshot around both Venus and Mars and then finally back to Earth. In addition, I was thinking that the craft itself should always need to keep its engine facing the sun so that a water layer could be kept between the astronauts and the solar radiation without needing to completely surround the ship. I'm working on a CAD model that I can post when it's done. Thanks for the feedback guys.

Sundancer has been cancelled. Also, you need a water layer covering the entire crew cabin- solar radiation is pushed in all directions, nbot just out, due to the solar mag. field.

[DBowman]

20 hours ago, Sarge00Seven said:

thinking that the craft itself should always need to keep its engine facing the sun so that a water layer could be kept between the astronauts and the solar radiation without needing to completely surround the ship.

 

1 hour ago, fredinno said:

Also, you need a water layer covering the entire crew cabin- solar radiation is pushed in all directions, nbot just out, due to the solar mag. field.

This is inconvenient but apparently so - often designs have a smaller 'storm shelter' for use during solar flares to keep the water mass down. You might also find you need to alter the craft attitude to the sun for solar arrays and/or controlling how much heat it picks up. Venus insolation is 2x (?) earth and Mars much less, good 'passive' thermal control will save you electric power.

[DBowman]

The venus flyby mission I referenced above mentions in passing that Apollo CSM used 1000 pounds of RCS fuel to do the luna mission, mainly the two rendezvous and some fine tuning I guess.