Seer - 22/3/2008 7:07 PM
Regarding your last point: in my scenario, one would only have to build one type of spacecraft, which would be refueled in earth orbit, instead of the normal 4 different habs/erv/mars ascent vehicles in other plans.
As for deriving water on mars - that would either come from underground ice or from manufacturing water from co2 and h2 feedstock brought from earth.
Jason - 17/3/2008 10:02 AM
How well would a book like Red Mars hold up to reality? Do the ideas in it have any basis in the scientific community or is it misleading?
scienceguy - 23/4/2008 10:50 AM
I know NASA's plan for the moon is to set up an outpost there. Does the VSE include an outpost on Mars as well? Have they planned that far in advance?
Can anyone describe the mission trajectory for a direct ascent option to the apollo missions?s
Also to my surprise a methane fuel option though I'd hate to see how many an ERV would need to get off Mars then again it can't be any worse then Falcon 9.
Not many people still cling to a Zubrin-esque ERV capable of supporting a crew from Mars ascent right through to landing on Earth.
A far more realistic concept is to have rendezvous in Mars orbit with the ERV. This reduces the launch mass of the Mars Ascent Vehicle to something like 15-25,000kg. Given the much lower gravity on Mars, one or two RL10s would be perfect for this application.
Recently it seems NTR and NEP missions such as BNTR have gained the upper hand over ISRU centered Mars missions.
The Mars ascent vehicle may still use ISRU and it's launch mass might be closer to 50T vs 25T of course the weight would be 1/3 on Mars.
I figure the most bare bones ascent vehicle would be an Orion CM and a methane ascent stage.
Mars's gravity well though less then Earth's is still much deeper then the Moon's.
I figure the Mars ascent vehicle also would need enough delta V to play an active role in seeking the MTV and docking with it in just a few days.
Also to my surprise a methane fuel option though I'd hate to see how many an ERV would need to get off Mars then again it can't be any worse then Falcon 9.
Not many people still cling to a Zubrin-esque ERV capable of supporting a crew from Mars ascent right through to landing on Earth.
A far more realistic concept is to have rendezvous in Mars orbit with the ERV. This reduces the launch mass of the Mars Ascent Vehicle to something like 15-25,000kg. Given the much lower gravity on Mars, one or two RL10s would be perfect for this application.
Recently it seems NTR and NEP missions such as BNTR have gained the upper hand over ISRU centered Mars missions.Not sure I follow you here. ISRU is not and cannot be a factor until you get there. NTR is most likely to be used for TMI so is compatible with any type of mission.QuoteThe Mars ascent vehicle may still use ISRU and it's launch mass might be closer to 50T vs 25T of course the weight would be 1/3 on Mars.How do you figure that? Do some maths. All you need is a cabin suitable for the four to six people most commonly assumed to make up the crew, and then a rocket stage to go under it. You can use scaled up numbers from the LEM ascent stage, or from the Soyuz BO, or whatever, to come up with the 'cabin' mass, and the main propulsion system ends up being a bit like an EELV upper stage. 50t is way too much.QuoteI figure the most bare bones ascent vehicle would be an Orion CM and a methane ascent stage.No it wouldn't. The Orion is pretty substantial, far heavier than necessary. The bare bones would be some sort of pressure-stabilised Al-Li sphere housing the crew. Or even an unpressurised Langley type design.QuoteMars's gravity well though less then Earth's is still much deeper then the Moon's.
I figure the Mars ascent vehicle also would need enough delta V to play an active role in seeking the MTV and docking with it in just a few days.
The MAV needs something like 4km/s delta-v to reach orbit (IIRC), vs. about 2.6km/s for the moon. IMHO the simplest design would have a single RL10-derived engine in the CH4/LOX main ascent stage, and then the crew capsule itself would have a small hypergolic RCS. The ascent stage would be jettisoned before attmepting to dock with the orbiting vehicle.
I was thinking the Orion CM because this is NASA we're talking about and they tend to prefer to error on the side of caution.
Plus NASA would want a few days of loiter time just in case the MAV is forced to launch with the MTV out of position.
Though there might be one advantage to using an Orion CM for the ascent vehicle the crew can leave the MTV for home once it's captured.
This also would allow the MTV to take a more leisurely trip back to LEO after capturing at one of the Earth/Moon liberation points.
It also could be used if something goes wrong and the MTV can't perform the Earth capture burn though the reentry speeds might be pretty close to Orion's limits but it's better then getting stuck up there.
You'd get the crew back and your biggest worry would be congress complaining they lost an expensive asset and the environmentalists complaining about a big nuclear space craft being in an Earth crossing orbit though the flyby can be designed in such a way it'll never return to earth for centuries.
As for an open ascent vehicle Mars does still have an atmosphere wouldn't it still be trouble?
Plus you'd be cutting your time from leaving the surface hab to rendezvous to under 9 hours the max limit a spacesuit can scrub CO2 and provide O2.
Theres the problem of entering and landing a heavy load thru the thin Mars atmosphere, but given the what you can throw at the problem - its workable - the first thing that pops into my mind are a serries of large, potentially bulky parachutes optimized for different velocities and altitudes to slow it down enough for a powered landing. Maybe it would make a Hab look like a 5 story tuna-can instead of a 3 story one. The point is with enough throw capability you could make the last parachute in the serries as large as it has to be in order to slow the vehicle down to the point where rockets can be fired for the landing.
Theres the problem of entering and landing a heavy load thru the thin Mars atmosphere, but given the what you can throw at the problem - its workable - the first thing that pops into my mind are a serries of large, potentially bulky parachutes optimized for different velocities and altitudes to slow it down enough for a powered landing. Maybe it would make a Hab look like a 5 story tuna-can instead of a 3 story one. The point is with enough throw capability you could make the last parachute in the serries as large as it has to be in order to slow the vehicle down to the point where rockets can be fired for the landing.
Parachutes aren't the answer. There's a really good paper on Mars EDLS that you can probably dig up off google.
Essentially, different methods of decelleration are useful at certain airspeed ranges. So, at the very top end, you need a robust heat-proof drag device (a heatshield) to withstand the very harshest point of entry. If that shield can provide sufficient drag in relation to the vehicle's mass, you have a chance of slowing sufficiently before hitting the surface, and you can deploy another drag device.
Historically, a supersonic parachute has been employed as the second drag device, and, again, this needs to impart sufficient decelleration to the vehicle in a short time so that the next system can be used- this is propulsive descent, which should only be used once you have reached subsonic speeds.
Once you are travelling subsonic you can fire retro-rockets which whatever thrust/impulse is necessary to do the job.
So, each drag device needs to slow the vehicle into the region where another type of system can take over, before it hits the surface.
Ballutes have been suggested as a bridge between parachutes and heatshields; inflatable heatshields have also been suggested. Lifting entry can help a bit too. It is likely that some combination of such technologies will be needed to enable manned missions.
Using current technology limits, the entry vehicle cannot have a 'density' (mass/heatshield area) of more than about 150kg/m2, of else it hits the surface before it has slowed enough to deploy a parachute. So for something using a 10m PLF this would mean an entry mass of less than 12t.
Well it would appear current technology is just not good enough for a manned mission then.
Well it would appear current technology is just not good enough for a manned mission then.
Well, actually it is (as far as entry and landing), we just don't have the cost-effective lift capacity to get enough mass to Mars to make it feasible.
Sure there is 2 J246s per mars direct component
If 10m payload fairing on a j246 limits a landable mass to 12mT and Zubrins idea of a Hab was 25mT then the current state of the art may not be good enough.
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Using current technology limits, the entry vehicle cannot have a 'density' (mass/heatshield area) of more than about 150kg/m2, of else it hits the surface before it has slowed enough to deploy a parachute. So for something using a 10m PLF this would mean an entry mass of less than 12t.
Quotetnphysics - 9/3/2008 8:11 PM
The second method may not work owing to speed-of-light communication delays (up to 20 minutes+)
It will work, it is called email
I ment telephone.
Well it would appear current technology is just not good enough for a manned mission then.
Well, actually it is (as far as entry and landing), we just don't have the cost-effective lift capacity to get enough mass to Mars to make it feasible.