Author Topic: Asteroid Retrieval Mission Concept  (Read 152729 times)

Offline Robotbeat

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Re: Asteroid Retrieval Mission Concept
« Reply #40 on: 06/30/2013 10:32 PM »
the House is trying to cut all funding.

There is no extant funding for this which they could "cut." Some in the House are trying to prevent the creation of any funding.
Right, and to prohibit any funding from going to the asteroid mission.

This pushes back the earliest possible mission, thus giving ammunition to those opposed to the asteroid mission... Self-fulfilling prophecy.

And that's the wonderful thing about brinksmanship on Capitol Hill. We end up going NOWHERE.
« Last Edit: 06/30/2013 10:35 PM by Robotbeat »
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Offline ChileVerde

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Re: Asteroid Retrieval Mission Concept
« Reply #41 on: 07/01/2013 02:02 PM »
the House is trying to cut all funding.

There is no extant funding for this which they could "cut." Some in the House are trying to prevent the creation of any funding.

I could easily be wrong, but I read Gerstenmaier's remark as stemming from technical and programmatic considerations, not the Hill's opposition to the ARM mission. That opposition, AFAIK, started manifesting itself seriously a few weeks after the April meeting in which he made the remark.
"I canít tell you which asteroid, but there will be one in 2025," Bolden asserted.

Offline Robotbeat

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Re: Asteroid Retrieval Mission Concept
« Reply #42 on: 07/01/2013 03:06 PM »
ChileVerde: your quote needs context. NASA is currently looking at two specific asteroids for the retrieval mission (though there are many other possibilities), and the best-understood earlier target (for which we have decent mass and spin-rate figures) can't be done unless stakeholders agree to it. The second target has been characterized less thoroughly right now.

Also, did Kennedy know which lunar landing site 12 years before Apollo 11? Obviously not, since he wasn't even elected, yet, nor was anything even in orbit, yet. I don't think they decided on a lunar landing site until sometime after Lunar Orbiter 1 in 1966, just 3 years before.
« Last Edit: 07/01/2013 03:17 PM by Robotbeat »
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Offline ChileVerde

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Re: Asteroid Retrieval Mission Concept
« Reply #43 on: 07/01/2013 03:51 PM »
ChileVerde: your quote needs context. NASA is currently looking at two specific asteroids for the retrieval mission (though there are many other possibilities), and the best-understood earlier target (for which we have decent mass and spin-rate figures) can't be done unless stakeholders agree to it. The second target has been characterized less thoroughly right now.

I knew they had constructed an exemplar mission using 2009 BD as a target, but not that they have actual candidate targets. Is 2009 BD one of the actual targets? A url would be appreciated.
"I canít tell you which asteroid, but there will be one in 2025," Bolden asserted.

Offline A_M_Swallow

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Re: Asteroid Retrieval Mission Concept
« Reply #44 on: 07/01/2013 06:31 PM »
I do not believe the mission will go to either of the two asteroids.  The spacecraft will almost certainly be late so it will have to go elsewhere.

With a lasso bag and medium sized SEP there is a lot of new technology to debug.  Delays of several years are likely.  When integration is finished we can look for a suitable asteroid in the following 2 or 3 years.

The astronomers can help by looking for candidates for each of the next 15 years.

Offline ClaytonBirchenough

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Re: Asteroid Retrieval Mission Concept
« Reply #45 on: 07/02/2013 03:26 AM »
Looks like they originally estimated the solar arrays, engines, and structure at 5000 kg ... when they realized they had another 995 kg available from the Atlas, they decided to use it.  Sounds reasonable to me.  :)

Re-examining, I'm not sure what I was thinking! Sounds reasonable to me now, and can't wait to see all that Xenon put to good use! Does any one have an estimate on how much Xenon costs per KG?
Clayton Birchenough
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Offline aero

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Re: Asteroid Retrieval Mission Concept
« Reply #46 on: 07/02/2013 03:39 AM »
Quote
Does any one have an estimate on how much Xenon costs per KG?

About $1200. Google is your friend, if you use it. 12,000 kg X $1200 / kg is $14.4 million. Fuel (or in this case, reaction mass) is cheap compared to the other costs of a space mission. Still, using Argon would save a few million dollars. At $5.00 per kg, 12,000 kg of Ar comes in at $60,000.
« Last Edit: 07/02/2013 03:48 AM by aero »
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Offline ClaytonBirchenough

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Re: Asteroid Retrieval Mission Concept
« Reply #47 on: 07/02/2013 03:54 AM »

About $1200. Google is your friend, if you use it. 12,000 kg X $1200 / kg is $14.4 million. Fuel (or in this case, reaction mass) is cheap compared to the other costs of a space mission. Still, using Argon would save a few million dollars. At $5.00 per kg, 12,000 kg of Ar comes in at $60,000.

Suppose I should not be lazy... Sorry.

What's the reason for using Xenon over Argon?
Clayton Birchenough
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Offline spectre9

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Re: Asteroid Retrieval Mission Concept
« Reply #48 on: 07/02/2013 04:14 AM »
Xenon works.

All about the TRL.

You'd spend that $14.4 mill in a couple of weeks trying to catch up in development with other propellants.

Offline Proponent

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Re: Asteroid Retrieval Mission Concept
« Reply #49 on: 07/02/2013 04:16 AM »
I don't know for sure what analysis the designers have done in choosing their propellant, but xenon has the advantages of a lower ionization energy, higher density and higher boiling point.

[rant]
Please note that the names of chemical elements, e.g., xenon and argon, are not capitalised.
[/rant]

P.S.  I could add that mercury, by these criteria, would be an even better propellant, but it tends to be highly reactive and winds up coating electrodes and such.
« Last Edit: 07/02/2013 04:18 AM by Proponent »

Offline Robotbeat

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Re: Asteroid Retrieval Mission Concept
« Reply #50 on: 07/02/2013 04:23 AM »
Xenon works.

All about the TRL.

You'd spend that $14.4 mill in a couple of weeks trying to catch up in development with other propellants.
Not just the TRL, it has lots of advantages. (Though, of course, TRL is pretty high on that list.)
« Last Edit: 07/02/2013 04:23 AM by Robotbeat »
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Offline aero

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Re: Asteroid Retrieval Mission Concept
« Reply #51 on: 07/02/2013 06:56 AM »
Is the VASIMR going to get its test on the ISS? It uses argon and has a much better efficiency than has been claimed for the proposed capture vehicle?

Fuel price only becomes significant when the vehicle is reused a few times. Using the same vehicle, or the same vehicle design a few dozen times makes that $14 M fuel bill start to add up.
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Offline Robotbeat

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Re: Asteroid Retrieval Mission Concept
« Reply #52 on: 07/02/2013 02:52 PM »
It's not just the fuel price. Using another propellant besides Xenon means storage is more difficult (i.e. heavier and/or more complicated), efficiency is lower, besides the fact that the TRL would also be lower.

And there are ways to reduce Xenon's cost if it came down to that.

The whole question of Xenon vs other propellants belongs in another thread.

The asteroid retrieval mission is either going to be using an array of gridded ion thrusters (such as NEXT, which has a rather high TRL and really, really good total efficiency--not to mention long demonstrated total life--but also probably too high of an Isp, a problem which would get much worse if you used Argon or Krypton, plus the efficiency would be lower and dry mass higher) or Hall thrusters (i.e. the 20kW units from JIMO, also being tested as we speak). And both would use Xenon.
« Last Edit: 07/02/2013 03:01 PM by Robotbeat »
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Offline aero

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Re: Asteroid Retrieval Mission Concept
« Reply #53 on: 07/02/2013 03:57 PM »
Quote
And there are ways to reduce Xenon's cost if it came down to that.

Could you elaborate on those ways? Xenon is exceedingly rare.

Just to be clear, I do not see a cost problem using Xenon in a one-off asteroid capture mission, or for one-off missions to the outer planets, for example. But if someone ever starts to reuse these tugs commercially to capture asteroids then the cost of the Xenon fuel counts. After all it costs more than 10% of the launch costs of the fuel launched for refueling the tug in LEO. (Say that launch vehicle costs $70 M, so the Xenon fuel payload is then 20% of the cost to refuel the tug in LEO.) That number becomes significant compared to the cost of bringing the TRL of other engines/fuels up to 8 - 10, in a reusable environment.

And don't throw out the ISRU argument, that solution  will cost way more and commercial enterprises will not pay for it until they are profitable and ISRU is proven.
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Offline ClaytonBirchenough

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Re: Asteroid Retrieval Mission Concept
« Reply #54 on: 07/02/2013 04:49 PM »
[rant]
Please note that the names of chemical elements, e.g., xenon and argon, are not capitalised.
[/rant]

Sorry haha.
« Last Edit: 07/02/2013 04:50 PM by ClaytonBirchenough »
Clayton Birchenough
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Offline A_M_Swallow

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Re: Asteroid Retrieval Mission Concept
« Reply #55 on: 07/02/2013 07:09 PM »
{snip}
The asteroid retrieval mission is either going to be using an array of gridded ion thrusters (such as NEXT, which has a rather high TRL and really, really good total efficiency--not to mention long demonstrated total life--but also probably too high of an Isp, a problem which would get much worse if you used Argon or Krypton, plus the efficiency would be lower and dry mass higher) or Hall thrusters (i.e. the 20kW units from JIMO, also being tested as we speak). And both would use Xenon.

On April 29, 2013 Busek Co signed SBIR contracts with NASA to develop 15 kW Hall effect thrusters.  Thrusters from Busek have used both argon and xenon as propellant.

As a general rule it is a lot cheaper to change things like the propellant at the start of a project than the end.  Early changes reduce the things that need doing twice.
http://halleffectthrusters.com

A Hall effect thruster using argon as its propellant.

Offline USFdon

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Re: Asteroid Retrieval Mission Concept
« Reply #56 on: 07/02/2013 07:35 PM »
I don't see this happening before 2025, by which time we may already have done em-2 thru em-5.

And speaking of that, I just noticed the following:

Quote
http://science.nasa.gov/media/medialibrary/2013/06/21/Minutes-NAC_Science_April_18-19-130620b-SIGNED.pdf

NASA Advisory Council Science Committee Meeting, April 18-19, 2013

<much snippage>

Mr. Gerstenmaier reviewed the interplanetary trajectory of the planned mission; 12 metric tons of xenon (Hall thruster) will be used to test its capability in terms of duration and impulse. Reaching the object will take 1.84 years and the traverse back to Earth 2.99 years.

<snip>

Responding to a suggestion to use a 2021 cruise mission for the mission, Mr. Gerstenmaier commented that the object cannot be obtained any sooner than 2024. However, HEOMD should be ready to launch to it by 2021. There is a calendar disconnect - this is a feasibility study only, not a mission design.

<much more snippage>

Now, these notes are distressingly gnomic, but I'd tentatively interpret them to mean that the Orion-asteroid rendezvous won't happen until 2024 at the earliest. As the present SLS launch schedule has EM-2 in 2021, EM-3 in 2023 and EM-4 in 2025, it would appear that EM-2, even though "ready" to go to the asteroid, won't have an asteroid to go to. Possibly the same for EM-3, though it might be delayed if an asteroid were indeed on the way. 

So what are EM-2 and possibly EM-3 to do?  I'd guess trips to DRO to practice for an actual asteroid rendezvous.

P.S.: Another implication is that the SEP asteroid-grabber probably won't launch before 2020, which seems reasonable.

Offline Robotbeat

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Re: Asteroid Retrieval Mission Concept
« Reply #57 on: 07/02/2013 08:13 PM »
You guys, of course you COULD use argon or krypton or whatever, and some of those were traded against xenon (krypton particularly), but it was quite definitely NOT worthwhile doing. New thread to discuss it for other missions. And again, it's not worth considering until the cost of launch gets in the range of $1000/kg. Right now, they're looking primarily at Atlas V, so far more than that.

Xenon's supply isn't limited because it is produced via fractional distillation of the air, not by a limited mineral resource or something.
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Offline Solman

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Re: Asteroid Retrieval Mission Concept
« Reply #58 on: 07/03/2013 06:27 PM »
Quote
And there are ways to reduce Xenon's cost if it came down to that.

Could you elaborate on those ways? Xenon is exceedingly rare.

Just to be clear, I do not see a cost problem using Xenon in a one-off asteroid capture mission, or for one-off missions to the outer planets, for example. But if someone ever starts to reuse these tugs commercially to capture asteroids then the cost of the Xenon fuel counts. After all it costs more than 10% of the launch costs of the fuel launched for refueling the tug in LEO. (Say that launch vehicle costs $70 M, so the Xenon fuel payload is then 20% of the cost to refuel the tug in LEO.) That number becomes significant compared to the cost of bringing the TRL of other engines/fuels up to 8 - 10, in a reusable environment.

And don't throw out the ISRU argument, that solution  will cost way more and commercial enterprises will not pay for it until they are profitable and ISRU is proven.

 I will throw out "the ISRU argument.
Concentrated sunlight directed to the surface of an asteroid will release volatiles that average 1 km/sec. A spacecraft that uses thrust to keep up with an asteroid onto which it is directing the energy would not even need to make physical contact with the asteroid.
 Such a spacecraft need not carry any propellant to be used for asteroid redirection.
 Cost/technical risk reduction makes sense for multi-billion dollar so TRL is vital but another way to reduce risk/cost is to reduce the project to a 3U cubesat or preferably many cooperating cubesats. This might allow high risk tech because you can learn from failure and build a second generation craft. Using a swarm of spacecraft helps as well.
By using the asteroid itself for reaction mass a few cubesats could have much more thrust than a SEP system using propellant from Earth. If mirrors anything like the L'Garde ones are used (17KW thermal/kg.) say 10KW per cubesat and four are used then both the keck concept and the cubesats have 40KW to use for producing thrust. Assuming that the efficiency of the ISRU system is 20% that of the Keck (a conservative guess) then we're comparing 40KW X .8(?)= 32KW at 3000+ sec. to 8KW at 100 or so sec. This means 900 times the thrust/5 = 180 times the thrust for the cubesats.
 Whether you use that or another ISRU based idea; ISRU is so wildly superior that cubesats can completely outclass a 15,000 lb. multi-billion dollar spacecraft. Makes me doubt that Xenon will ever be used commercially but then I would have never thought the ARM would be taken seriously either.   

Offline A_M_Swallow

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Re: Asteroid Retrieval Mission Concept
« Reply #59 on: 07/03/2013 06:37 PM »
Even solar thermal engines need a throat and nozzle.  A weird shaped combustion chamber can lead to instabilities.  So just heating a rock is unlikely to work very well.

Having a drill convert the asteroid into a powder that is feed into the engine may work.  This can be tested on Earth.

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