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NEO Mission Q&A
by
beancounter
on 06 May, 2010 02:04
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With all the hoo-ha about returning to the moon or not, the latest 'fad' seems to be an asteroid mission.
What I'd like explained is what makes an asteroid mission so attractive in comparison to a moon mission? Is it easier or harder and either way, why?
On the other hand, does it have to do with what might be discovered in the mineralology or chemical makeup of an asteroid and have nothing to do with the challenges of actually getting their, landing, and getting back?
As you can tell from my tag, I'm not a rocket scientist but can follow reasonably technical discussions on delta v, etc. so don't hold back.
Cheers,
Beancounter from downunder
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#1
by
Rabidpanda
on 06 May, 2010 05:45
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I'll list some possible reasons:
-Asteroids are filled with usable resources like metals, while the Moon has almost none.
-There is always the danger of an asteroid strike on Earth and experience getting to an asteroid could be useful.
-An asteroid mission would be reasonably long term, probably about 6 months, that's good practice for a Mars mission.
-We've already been to the Moon, an asteroid mission would be new and exiting to the public.
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#2
by
beancounter
on 06 May, 2010 07:09
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Thanks for that.
Seems to me that an asteroid mission is going to be quite a different beast to a moon mission for the following reasons:
1. Got to find a suitable one first - size, orbit, velocity, etc
2. Got to have a suitable vehicle or rather vehicles.
3. Got to get out to the asteroid, match velocities, spin, etc.
4. Land and somehow tether you ship and self to said asteroid.
5. Do whatever you want to do - testing, samples, etc
6. Launch off the asteroid.
7. Work out where the hell you've got to in relation to Earth.
8. Calculate your return journey although knowing the asteroid's orbit probably gets points 7 and 8 done before hand but still need to be able to recalculate if necessary - say you lost touch with Earth Mission Control somehow!
9. Get back into Earth orbit.
10. Get back to Earth.
Seems like there's a whole lot more to an asteroid mission than to say, a Mars mission. Lots more unknowns. Since NASA hasn't been able to develop a cost-effective vehicle to get back to the Moon, what chance for this latest effort?
Notice I finished with a question.
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#3
by
hop
on 06 May, 2010 07:48
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Thanks for that.
Seems to me that an asteroid mission is going to be quite a different beast to a moon mission for the following reasons:
1. Got to find a suitable one first - size, orbit, velocity, etc
2. Got to have a suitable vehicle or rather vehicles.
Unlike a Moon or Mars mission, you only need one type of vehicle.
3. Got to get out to the asteroid, match velocities, spin, etc.
Solved problem, we've done it with robots (NEAR, Hayabusa).
4. Land and somehow tether you ship and self to said asteroid.
Easier in many ways than the moon. Some interesting challenges, but tethering is probably not required, inertia combined with a very slight gravity will keep the ship in place. One big advantage is that it is slow and forgiving. If something goes wrong in a moon landing, you are in deep trouble. On an asteroid mission, you can probably back off and try again.
5. Do whatever you want to do - testing, samples, etc
EVAs may be tricky without enough gravity to walk and no handrails.
6. Launch off the asteroid.
MUCH easier than the moon.
7. Work out where the hell you've got to in relation to Earth.
8. Calculate your return journey although knowing the asteroid's orbit probably gets points 7 and 8 done before hand but still need to be able to recalculate if necessary - say you lost touch with Earth Mission Control somehow!
Navigation is a solved problem. The orbit of the target will be VERY well known before you get there, and even better known once you've landed on the surface.
9. Get back into Earth orbit.
10. Get back to Earth.
No need to get back into orbit. Direct entry is fine.
Seems like there's a whole lot more to an asteroid mission than to say, a Mars mission.
Incorrect.
1) Mars EDL and ascent to orbit are huge challenges, and a major portion of the development cost of a Mars mission. They also multiply the launch mass by a huge factor.
2) Mars has a very long minimum mission time, well beyond current experience. NEOs offer an intermediate step.
3) Mars is very difficult to do without nuclear power on the surface. An asteroid mission can be all solar, which will cut development cost.
4) Mars requires developing a long lived deep space craft and surface systems. A NEO mission requires only the deep space craft, and the early missions can be shorter.
5) NEO missions are amenable to high efficiency propulsion. A Mars mission needs high thrust for several stages, while a NEO mission could get by with having it only for Earth departure.
Overall a NEO mission should be much easier than a Mars mission. Phobos or Deimos would be pretty similar to a NEO mission, but the minimum mission time would be longer.
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#4
by
Robotbeat
on 06 May, 2010 15:45
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Yeah, the technical minimum to land and take off from an asteroid is pretty low... You could do it with a Manned Maneuvering Unit (or one that uses hydrogen peroxide for more delta-v) from a spacecraft in orbit around the asteroid. Also, just the RCS thrusters on a spacecraft like Orion have enough thrust to land and take off from an asteroid (the size of Phobos, for instance). You could probably land and takeoff in an unmodified Orion in an emergency. It's been done by robotic probes not designed for landing, so with the faster, real-time responses possible with a manned spacecraft, it should be easier (though it would be wise to make landing nominally automatic).
Much easier technical requirements than landing in a big gravity well.
The escape velocity of Phobos is only 11.4 m/s. An MMU can typically do about 24 m/s.
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#5
by
bodge
on 06 May, 2010 16:14
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4. Land and somehow tether you ship and self to said asteroid.
Easier in many ways than the moon. Some interesting challenges, but tethering is probably not required, inertia combined with a very slight gravity will keep the ship in place. One big advantage is that it is slow and forgiving. If something goes wrong in a moon landing, you are in deep trouble. On an asteroid mission, you can probably back off and try again.
5. Do whatever you want to do - testing, samples, etc
EVAs may be tricky without enough gravity to walk and no handrails.
If it's a ferrous rock, perhaps you could use magnets to hold you down
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#6
by
Aeroman
on 06 May, 2010 16:44
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Here is another question about an asteriod mission:
Would the spacecraft affect the orbit of the asteriod. I know that using a spacecraft to alter an asteroids orbit was one of the ways to move an asteroid away from impacting Earth.
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#7
by
beb
on 06 May, 2010 17:10
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The chief attraction for an asteroid mission is that you don' t need to develop a landing craft. So while an asteroid mission will be months longer than a lunar mission it will be cheaper because all you need is Orion and a launch vehicle. (to be determined later.)
Note that the President also talked of rendezvous with Phobos as a goal rather than landing on Mars. While the science seems thin on the ground, the costs are within something the US could attempt.
It's doubtful that any interesting amounts of minerals will be found during an asteroid mission but the structure of the rock could tell us a lot about how asteroids are formed and that in turn about how planets were formed.
One has only to look at how hard it is to do simple tasks assemblying the ISS to realize that something as unplanable and chaotic as mining an asteroid out of the question.
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#8
by
hop
on 07 May, 2010 00:52
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Note that the President also talked of rendezvous with Phobos as a goal rather than landing on Mars. While the science seems thin on the ground, the costs are within something the US could attempt.
The science could be pretty good
- Phobos is scientifically interesting in it's own right. It looks like a C or D type asteroid, but we're not sure how it got there.
- There are undoubtedly bits of Mars on Phobos, so you'd probably get some Mars sample return for free.
- Phobos would be a good base for tele-operated exploration (and/or future manned landing site prep) on Mars. Real time tele-operation would let you work a lot more quickly than our current robotic methods. Phobos would provide more radiation shielding than you'd be able to send on a stand alone orbiter. On the downside, you'd end up with a very long time spent in microgravity. It seems doubtful that Phobos gravity is sufficient to stop bone degeneration.
This would also be a reasonable stepping stone to an eventual surface mission.
One has only to look at how hard it is to do simple tasks assemblying the ISS to realize that something as unplanable and chaotic as mining an asteroid out of the question.
Certainly mining would be out of the question for the initial missions, but I don't see any reason to think it is inherently impossible.
Here is another question about an asteriod mission:
Would the spacecraft affect the orbit of the asteriod. I know that using a spacecraft to alter an asteroids orbit was one of the ways to move an asteroid away from impacting Earth.
Of course it would alter it, but only by a very minuscule amount. The proposal for changing asteroids course with a "gravitational tug" involves hovering near the asteroid for a long time.
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#9
by
Garrett
on 15 Jun, 2010 14:13
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5. Do whatever you want to do - testing, samples, etc
EVAs may be tricky without enough gravity to walk and no handrails.
Was just thinking about EVA's on an asteroid, so a quick search brought up this thread. Any info out there on work already done regarding EVA's "on" an asteroid? Something tells me that it would be a lot like an EVA on the ISS. Would they try to fix "handrails" to the asteroid?
I often wonder whether the astronauts would even feel the gravity? For example, on Itokawa, the gravity is a 1000 times less than on Earth!
Cheers,
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#10
by
hop
on 15 Jun, 2010 17:23
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Something tells me that it would be a lot like an EVA on the ISS. Would they try to fix "handrails" to the asteroid?
How you do that on a dirty rubble pile is unclear.
I often wonder whether the astronauts would even feel the gravity? For example, on Itokawa, the gravity is a 1000 times less than on Earth!
Closer to 1/100000th. Itokawa is very small, larger targets are possible, but obviously the larger sizes are rarer. Things would still have a noticeable tendency to drift toward the surface, but with an escape velocity of ~20cm/s losing stuff would be quite easy.
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#11
by
gin455res
on 25 Apr, 2012 22:04
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Are there as many NMOs and NVOs (near mars objects, and near venus objects) as there are NEOs?
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#12
by
neilh
on 25 Apr, 2012 23:40
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Are there as many NMOs and NVOs (near mars objects, and near venus objects) as there are NEOs?
While googling for an answer I came across this super-fascinating video of the locations of asteroids found in the solar system between 1980 and 2011:
http://www.youtube.com/watch?feature=iv&v=ONUSP23cmAEVenus seems to have fewer, but Mars seems to have quite a few (aside from the main asteroid belt).
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#13
by
Robotbeat
on 26 Apr, 2012 03:38
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Remember that near Venus objects are a lot harder for us to see (from the ground especially). But I certainly think Venus has fewer than Earth. And Mars has lots, of course (lots just sitting exposed on the ground, with enough atmosphere to slow them to terminal velocity but not so much as to have as extensive weathering and a biosphere, etc, which tends to bury them or destroy them on Earth.
EDIT:And that's a really great video... Thanks for posting! Over the course of 30 years, the number of known asteroids increased by almost two orders of magnitude... We knew of 60 times more asteroids in 2010 than we did in 1980! And according to surveys, there should be 25 million asteroids that are greater than 100m in diameter.
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#14
by
gin455res
on 26 Apr, 2012 06:11
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thanks neil.
By the end of the video there appears to be 2 donuts of asteroids; the main belt and one around earth's orbit.
I take it this earth-radius-donut is a bias resulting from asteroid spotting telescopes being located on (or in orbit around) earth, and caused by the relative ease with which smaller asteroids that are close to the earth can be observed?
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#15
by
Danderman
on 25 May, 2012 20:36
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Two questions for the price of one:
1) Why don't space probes that are headed to the outer solar system or Mars use their telescopes during the cruise phase to check for NEOs along their flight path?
2) If you want to not just flyby but rendezvous with a NEO, don't electric drives have a built-in advantage that, due to their long firing period, a circularization component to the thrust can be slowly added, so that by the end the cruise phase, the spacecraft is flying in a similar orbit as the target NEO?
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#16
by
ugordan
on 25 May, 2012 21:35
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1) Why don't space probes that are headed to the outer solar system or Mars use their telescopes during the cruise phase to check for NEOs along their flight path?
Their instruments are typically not sensitive enough and fields of view too small to cover any significant sky area in a reasonable time. Also, bandwidth and planning costs, etc. Ground surveys can still do a better job than your typical spacecraft imager.
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#17
by
strangequark
on 25 May, 2012 21:48
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2) If you want to not just flyby but rendezvous with a NEO, don't electric drives have a built-in advantage that, due to their long firing period, a circularization component to the thrust can be slowly added, so that by the end the cruise phase, the spacecraft is flying in a similar orbit as the target NEO?
You wouldn't add a circularization component so much as that is the natural transfer trajectory anyway. For most missions, the trajectory can be considered as a quasi-circular orbit with a gradually increasing radius.
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#18
by
Danderman
on 25 May, 2012 23:18
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2) If you want to not just flyby but rendezvous with a NEO, don't electric drives have a built-in advantage that, due to their long firing period, a circularization component to the thrust can be slowly added, so that by the end the cruise phase, the spacecraft is flying in a similar orbit as the target NEO?
You wouldn't add a circularization component so much as that is the natural transfer trajectory anyway. For most missions, the trajectory can be considered as a quasi-circular orbit with a gradually increasing radius.
OK, the drive could gradually increase the radius beyond the normal trajectory provided by a chemical rocket, right?
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#19
by
yinzer
on 26 May, 2012 01:06
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Mmm, not so much that electric propulsion has an advantage but more that the normal disadvantages of electric propulsion don't exist.
When trying to rendezvous with a planet, you need much less delta-v if you can accelerate at the bottom of a gravity well. It's called the Oberth Effect. The lower delta-v cam counteract the lower specific impulse of chemical propulsion. Of course you don't spend much time at the bottom of the gravity well so you need a higher T/W than you can get with electric propulsion.
When doing a rendezvous with an asteroid there's no gravity well to take advantage of, higher T/W doesn't really help, and electric propulsion's higher specific impulse means you need less propellant.
