Missions to Mars Q&A

[alexterrell]

Reading DRM5 and similar, I see that as in Apollo only thing that returns to Earth is the crew capsule. Six or seven monstrous Ares V launches; over thousand tons IMLEO and you recover and reuse nothing. Ok the hab stays on Mars; if you want your eventual second mission to go to very same place the first one did.
How much would departure vehicle mass IMLEO grow if you wanted to
return entire vehicle to say L1?

I understand there is very extreme and very widespread hatred for anything that can be mocked with "Battlestar" tag; but is it really economic to build thousand ton vehicles that cost tens of billions and then throw away every single part of them during one mission.

It should be possible with aerocapture, but I'm not sure if this has ever been done - though it should work.

My Mars reference plan (and I'm beyond version 5), now has SEP tugs carrying everything to L1, then depart from L1 (chemical) before aerocapture into Mars orbit. Then depart from Mars orbit and Aerocapture in Earth Orbit with rendez-vous again at L1.

[Robotbeat]

I suppose the empty Mars Transfer Vehicle (in a heliocentric orbit) could be captured by a SEP tug and brought back to EML1. You'd probably want to launch the SEP tug on a rendezvous trajectory before the crew even left the MTV (perhaps even before the crew left Mars).

For a MTV of ~100 tons and with ~4km/s to get it from its heliocentric trajectory to EML1, you'd need a SEP tug with a dry mass of ~10 tons, ~20 tons of fuel, given state-of-the-art solar and electric propulsion technology (and about half a year of thrusting with a 500kW solar array). Probably just as doable with a larger delta-v, it'd just take longer (it's going to take a while for the MTV to circle back to Earth, anyways).

[hyper_snyper]

I've been thinking about Mars mission architectures recently.

If you launch a bunch of cargo landers to Mars how hard would it be to get them to land relatively close to one another (say < 5 km).  So astronauts on the surface can get to them.  Assume heat shield, parachute, rocket propulsion for entry, descent, and landing.

What kind of navigation system would this entail?  INS, of course but what else?  Something like a homing beacon (akin to ILS in aviation) maybe?   

Is this an open problem?  If not, I'd like to read up on what ideas people have about doing precision landings on another world with no nav aids.

[JayP]

I've been thinking about Mars mission architectures recently.

If you launch a bunch of cargo landers to Mars how hard would it be to get them to land relatively close to one another (say < 5 km).  So astronauts on the surface can get to them.  Assume heat shield, parachute, rocket propulsion for entry, descent, and landing.

What kind of navigation system would this entail?  INS, of course but what else?  Something like a homing beacon (akin to ILS in aviation) maybe?   

Is this an open problem?  If not, I'd like to read up on what ideas people have about doing precision landings on another world with no nav aids.

Have enough delta V to place the lander in orbit before PDI instead of a direct entry fromthe transfer orbit and use a lifting reentry like the MSL will. You could also land a pathfinder payload with a homing beacon first and use that as a nav aid.

[Jackspace]

Would the Space X Dragon be a good mars lander, and only a lander.

[Dalhousie]

I ment telephone.

Polar explorers managed without telephones until quite recently, and often spent years away from their families. Submariners manage without telephones, even today. 

People on a Mars mission will have email, video messages, voice messages, and probably something like twitter and SMS.  Compared with previous explorers they will live in luxury.

[kkattula]

...  If not, I'd like to read up on what ideas people have about doing precision landings on another world with no nav aids.

I suggest landing a rover first, preferably tele-operated from orbit (Phobos?), that would survey a landing site, place several radio beacons around the site to allow precision landing, and even clear small rocks. 

Give the rover a bulldozer attachment (or land a separate ROV bulldozer) and clear a nearby base area. Give the landers wheels, and the rover could tow each one to the base area. Maybe even deploy some equipment, hook up comms & power cables etc.

[baldusi]

How can I calculate the pressure of the Marsian wind at a given altitude? I'm wondering what sort of strain it would put on a vertical solar panel, and if it would work as a sail. I've seen that most if not all solar powered devices on Mars have used mostly horizontal solar panels. So I'm wondering if wind pressure is an issue, or is simply avoiding to actually point the panel in the Sun's direction.

[su_liam]

How many cycler stations in Hohmann orbits would be required to allow for reliable available at all windows(every 780 days, I think)?

Would it be reasonable to put up cycler stations on more eccentric/faster orbits, such that one would be able to facilitate Earth/Mars transit on similarly or more frequent time windows?

Thanks.

[Hop_David]

How many cycler stations in Hohmann orbits would be required to allow for reliable available at all windows(every 780 days, I think)?

Would it be reasonable to put up cycler stations on more eccentric/faster orbits, such that one would be able to facilitate Earth/Mars transit on similarly or more frequent time windows?

Thanks.

Depends on what cycler you use. There's an Aldrin cycler that flies by earth and Mars each synodic period (roughly 2 1/7 years). But the line of apsides must be substantially rotated each orbit. And it zooms by Mars orbit at a pretty good angle, so the taxis moving between Mars and the cycler would have a steep delta V budget. So in terms of delta V, this cycler's not so good.

More Hohmann like are the Niehoff VISIT 1 and VISIT 2 cyclers. Their periods are 1.25 years and 1.5 years. (Period of an Earth Mars Hohmann ellipse is about 1.4 years). Less delta V for orbit maintenance as well as less for taxi rendezvous. Planetary fly bys more infrequent, though.

With a synodic period of about 2 1/7 years, you can see 7 synodic periods are about 15 years. But 7 periods isn't exactly 15 years, more like 14.95 years, so constant tweaking would be needed.

Venus is much more amenable to cyclers. Earth Venus synodic period is 1.5987 years, quite close to 1 3/5. 5 synodic periods is 7.993 years, very close to an 8 year cycle. What's more is an earth Venus Hohmann ellipse has a period of .7998 years, very close to 4/5 of a year. This makes for a 5 pointed star where the cyclers are traveling nearly Hohmann orbits.


 

[clongton]

Cyclers would be a great way to supply a base. The transfer points could be EML-2 and Phobos for Mars and EML-2 and HVO for Venus.

[guckyfan]

Cyclers would be a great way to supply a base. The transfer points could be EML-2 and Phobos for Mars and EML-2 and HVO for Venus.

Actually they are not at all suited for cargo. They don't give any delta-v for free. Getting something to the cycler and from there to the destination will require more delta-v than flying direct. It is worth it only if you save on mass which you cannot do with cargo.

What they do is give astronauts a habitat for the transfer so you save the mass of the habitat. Even that may not be enough to justify a cycler unless it has equipment for water and air recycling and maybe even food production which would save a lot of mass in supplys to launch with the astronauts.

[guckyfan]

I am trying to understand different possible mission profiles.

Frequently missions are proposed using L-points as staging points for missions to Mars. It seemed plausible to me. But then I found out about the Oberth-Effect and found some interesting delta-v charts for missions to the Moon, to Mars, and to Venus.

So getting to any L-point requires as much delta-v as direct transfer to Mars on a Homann-Trajectory. It looks to me as if using L-points for staging missions could be worth it only if using both SEP-tugs from LEO to the L-point and lunar fuel assuming quite low cost for both. And even then the advantage would not be very big compared to launching directly from LEO.

Am I missing something here?

[mmeijeri]

I am trying to understand different possible mission profiles.

Frequently missions are proposed using L-points as staging points for missions to Mars. It seemed plausible to me. But then I found out about the Oberth-Effect and found some interesting delta-v charts for missions to the Moon, to Mars, and to Venus.

You can still use the Oberth effect together with Lagrange points. The general idea is to drop from a Lagrange point to LEO altitude (perhaps with a lunar flyby) and then do a powered flyby to Mars.

So getting to any L-point requires as much delta-v as direct transfer to Mars on a Homann-Trajectory.

Considerably less than Mars, 3.2km/s - 3.8km/s depending on how long your trip is allowed to be. In addition, since EML1/2 is close to Earth you can use it as an assembly point, which means you can launch individual modules that will fit on a Centaur or DCSS instead of needing a huge EDS. You couldn't do that in Mars orbit, because the trip to Mars orbit takes far too long for that to be practical.

It looks to me as if using L-points for staging missions could be worth it only if using both SEP-tugs from LEO to the L-point and lunar fuel assuming quite low cost for both. And even then the advantage would not be very big compared to launching directly from LEO.

SEP and ISRU would add to the utility of Lagrange points, which is large to begin with.

[guckyfan]

You can still use the Oberth effect together with Lagrange points. The general idea is to drop from a Lagrange point to LEO altitude (perhaps with a lunar flyby) and then do a powered flyby to Mars.

That would involve two more passes of the VanAllen Belt. I don't think that would be a good idea especially for manned flights. Also it would require a lot of delta-v eating up much of the Oberth-Effect advantage. I can't really calulate that though so I cannot be positive on this.

So getting to any L-point requires as much delta-v as direct transfer to Mars on a Homann-Trajectory.

Considerably less than Mars, 3.2km/s - 3.8km/s depending on how long your trip is allowed to be. In addition, since EML1/2 is close to Earth you can use it as an assenbly point, which means you can launch individual modules that will fit on a Centaur or DCSS instead of needing a huge EDS. You couldn't do that in Mars orbit, because the trip to Mars orbit takes far too long for that to be practical.

The two charts I have seen both showed more delta-v for L-points than for a Homann-trajectory to Mars. Even a geostationary Orbit needs more.
You can assemble the modules in LEO which may be a good idea anyway even if you then lift them with SEP tugs afterwards.

Edited to correct quote nesting