### Author Topic: Mission to earth Trojan asteroid, 2010Tk7  (Read 6115 times)

#### faramund

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##### Mission to earth Trojan asteroid, 2010Tk7
« on: 01/13/2014 04:48 AM »
2010Tk7 (http://en.wikipedia.org/wiki/2010_TK7) is a 300m diameter asteroid at Earth's L4 point. Wiki claims that it takes less energy to get to L4, then the moon, although I assume it would take somewhat more time.

So.. what advantage would there be to going to a small asteroid in orbit around the moon, in comparison to going to it? Is it just time? Can anyone do the orbital calculations to say how long it would take to get to it (and back)?

Well, actually, on further reading, it seems that 2010_TK7, is in a poor inclination and so would take more deltaV to get to, than going to Lunar orbit, so that probably largely answers my own questions...

« Last Edit: 01/13/2014 04:54 AM by faramund »

#### QuantumG

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #1 on: 01/13/2014 04:54 AM »
Read the "Accessibility from Earth" section in the wikipedia article you linked.
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#### faramund

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #2 on: 01/13/2014 05:27 AM »
Read the "Accessibility from Earth" section in the wikipedia article you linked.

I did, which is why I added the third paragraph (well, after I tried to delete the topic, and discovered I couldn't).

But its still interesting, if 2010Tk7 is 300m in diameter, and was only found 3-4 years ago, then there's probably other asteroids at either L4 or L5 that are smaller than that, and that potentially have better inclinations, and that hence would be easier to get to than lunar orbit.

Although, it seems difficult to find out whether they exist or not, and I still don't know what the difference in travel time would be.

#### aero

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #3 on: 01/13/2014 05:41 AM »
It takes a little delta V to get to the actual L4 or L5 point, but it takes a long time. After all, the points are 1 AU away from earth. 150 million km at 1 km/s would be 1.5E8 seconds if you could go in a straight line.  And you need to get to C3 speed first so count that delta V, too. Then stopping would be another 1 km/s.

That's about 5 years but you'd probably use a Lunar gravity assist to get you there in about 10 months. But then you have to stop if you want to see anything so that'd be what, about 5 km/s to stop at the Lagrange point.

The Stereo spacecraft did it, fly-bys, you could try to find out about that program.

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#### Ben the Space Brit

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #4 on: 01/13/2014 03:15 PM »
That's something that's always bothered me... well, 'bothered' is too strong a word - it's something of which I've been aware... the difficulty inherit for a crewed spacecraft in matching orbits with the target objects. Most of the NEA candidates have only theoretical gravitation, so the visitor spacecraft has to do something more like matching orbits rather than orbit the target object itself. That would take a lot of delta-v and it's one of the elephants in the room about doing an NEA encounter mission: You're going to end up needing as much if not more propellant than a Mars mission.

Even using an electric engine means that you would have to commit to a multi-year cruise spending possibly as much as a year slowly matching orbital trajectory and speed with the target object.
« Last Edit: 01/13/2014 03:15 PM by Ben the Space Brit »
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#### aero

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #5 on: 01/13/2014 03:49 PM »
I've been thinking (danger danger), wouldn't it be easier and/or quicker to go to the Mars Trojans at Mars L4, L5 than Earth L4, L5? We know that the Mars Trojan asteroids exist because the lighting is such that we can see them through telescopes from earth. Any Earth Trojan asteroids aren't lighted very well for viewing from the angle of earth viewing.

Have any big telescopes looked for Earth Trojan asteroids?
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#### Hop_David

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #6 on: 01/13/2014 04:04 PM »
Most of the NEA candidates have only theoretical gravitation, so the visitor spacecraft has to do something more like matching orbits rather than orbit the target object itself. That would take a lot of delta-v and it's one of the elephants in the room about doing an NEA encounter mission: You're going to end up needing as much if not more propellant than a Mars mission.

No, rendezvous with an NEA can done with much less delta V than a Mars mission.

#### Danderman

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #7 on: 01/14/2014 02:32 AM »
Quote
I've been thinking (danger danger), wouldn't it be easier and/or quicker to go to the Mars Trojans at Mars L4, L5 than Earth L4, L5?

As mentioned before, these are easy to fly by, really, really hard for rendezvous due to high approach velocities.
« Last Edit: 01/14/2014 02:32 AM by Danderman »

#### kkattula

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #8 on: 01/14/2014 03:01 AM »
If you want to visit a decent sized asteroid, we know where there are a couple of them in accessible orbits:

- 12 & 22 km in diameter
- 2.5 km/s beyond escape including rendezvous (approx 1.5 km/s to go from one to the other)
- 7 month transit time each way (plus 18 months wait for a return window)
- launch window approx every 2 years
- interesting views

« Last Edit: 01/14/2014 03:02 AM by kkattula »

#### Robert Thompson

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #9 on: 01/14/2014 04:56 AM »
"It is possible that Stickney is large enough to be seen with the naked eye from the surface of Mars." wiki
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#### JohnFornaro

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #10 on: 01/14/2014 01:46 PM »
So... what advantage would there be to going to a small asteroid in orbit around the moon, in comparison to going to it? Is it just time?

For some reason, the speculation around here centers on low delta-vee, and you will find little information regarding the time it takes to get from point a to point b.

I struggle with this handwaving away of mission time, since it is costly in mass and dollars to feed, water, and oxygenate your astros for longer and longer periods of time.  Rmember also, that they need to come back home and that mission control needs to be funded as well.

There is also the  delta-vee necessity of orbiting a body which has negligible gravity, as Ben pointed out above.
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#### kkattula

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #11 on: 01/14/2014 03:09 PM »
So... what advantage would there be to going to a small asteroid in orbit around the moon, in comparison to going to it? Is it just time?

For some reason, the speculation around here centers on low delta-vee, and you will find little information regarding the time it takes to get from point a to point b.

That's because beyond a certain point the tyranny of the exponential in the rocket equation turns delta v into mass, and we can do the math.

Quote
I struggle with this handwaving away of mission time, since it is costly in mass and dollars to feed, water, and oxygenate your astros for longer and longer periods of time.  Remember also, that they need to come back home and that mission control needs to be funded as well.

With moderate recycling, food, water & oxygen can be less than 1 kg per crew per day. Even for multi-year missions, orders of magnitude less than the propellant required by high delta v, short duration trips. Multi-year mission control is a tiny fraction of current development & launch costs

Quote
There is also the  delta-vee necessity of orbiting a body which has negligible gravity, as Ben pointed out above.

Orbiting one is no problem, you can even just park next to it and use a small electric thruster for occasional position hold.

AIUI, what Ben was talking about is matching solar orbits with an asteroid. Unlike a planet, you can't use orbital velocity around the body to 'cheat' a large chunk of that delta v.

Although if there happens to be a handy planet nearby... (cough Phobos/Deimos cough)

#### faramund

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##### Re: Mission to earth Trojan asteroid, 2010Tk7
« Reply #12 on: 01/14/2014 06:41 PM »
So... what advantage would there be to going to a small asteroid in orbit around the moon, in comparison to going to it? Is it just time?

For some reason, the speculation around here centers on low delta-vee, and you will find little information regarding the time it takes to get from point a to point b.

I struggle with this handwaving away of mission time, since it is costly in mass and dollars to feed, water, and oxygenate your astros for longer and longer periods of time.  Rmember also, that they need to come back home and that mission control needs to be funded as well.

There is also the  delta-vee necessity of orbiting a body which has negligible gravity, as Ben pointed out above.

I wasn't ignoring time, I just knew that was a potential issue, and was trying to find any other issues. I could also add, that I was also trying to get advice on quantifying the time figure.

My assumptions are now .. 2010Tk7 would cost more in deltaV to get to, in comparison to moon orbit.

There could be other masses at L4 or L5 that could take less deltaV to get to, but probably only on a slow trip. That time could be reduced, but then the deltaV required will be increased, and at some point will be more than lunar orbit.

The one area I think that the L4 or L5 points could still come in useful (well in this context), would be to find potential small candidates to move to lunar orbit, in contrast to moving an LEO to lunar orbit. But at least at the moment, there are none that we know of.

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