3
$\begingroup$

There is a planned launch from SpaceX called Polaris Dawn; for a modified Dragon capsule, currently planned for early summer 2024, with the ability to depressurize and allow astronauts to do a space walk in versatile special spacesuits designed by SpaceX called Polaris Dawn.

This new ability should open up a door to things which were previously impossible to do. What can we do with this new feature?

Could it be used to allow astronauts to explore near Earth asteroids, such as Apophis, and do some rudimentary asteroid mining with the help of a Dragon capsule which can carry up to 4 people for such mission to perform EVAs. The asteroid gravity would be close to zero, so it would require minimal fuel to dock with asteroid.

Maybe asteroids could also be useful for collecting insitu resources or for growing plants?

$\endgroup$
7
  • 10
    $\begingroup$ “This new ability”? People have been climbing out of space craft since 1965. And these suits aren’t anywhere near as capable as those used on the ISS for decades. $\endgroup$ Commented May 12 at 19:58
  • 3
    $\begingroup$ Thanks. Correction, new ability for the Dragon capsule. $\endgroup$
    – estinamir
    Commented May 12 at 20:01
  • 3
    $\begingroup$ Any such mission would take many months. Dragon lacks that endurance. $\endgroup$
    – John Doty
    Commented May 12 at 21:01
  • 2
    $\begingroup$ You might be interested in this paper exploring what a manned mission to Apophis might look like. In the end, they spend 1 day on Apophis and admit that "Obviously, the scientific part of the stay of one or two astronauts on Apophis will have to be reduced to a minimum, leaving an important role for media and communication constraints." $\endgroup$
    – Cort Ammon
    Commented May 13 at 3:30
  • 4
    $\begingroup$ There isn't much humans can do on an asteroid a probe can't do. By saving on the weight of the passengers and life support, a mission can bring much more scientific instruments, or use a much cheaper launcher. That's not even taking into account the savings obtained by taking a longer route (gravity assist, etc...) and the risk of losing the crew's lifes. There isn't much reason to do a crewed mission to an asteroid right now. $\endgroup$
    – armand
    Commented May 13 at 5:40

2 Answers 2

12
$\begingroup$

You might be over-estimating the significance of these new EVA suits. They are designed to provide brief protection to exposure to full vacuum. The advance on the previous SpaceX intra-vehicular suits is that they can allow people to actually deliberately exit the spacecraft, rather than just withstand an unintended loss of pressure within the craft. However:

  • They are not autonomous (astronauts must be tethered to the ship to provide oxygen, power, and so on). So they are less capable than the suits used on the ISS.
  • They currently do not provide leg mobility - they are designed just to allow people to float in space, not walk on a surface. So they are less capable than the suits used on Apollo, or those being designed for Artemis.

With many products at SpaceX, however, the design process is iterative rather than going straight to the end solution, as we have seen with the evolution from the IVA to EVA suits. So increases in capability are certainly possible over time.

Meanwhile, the constraints on asteroid intercepts are more about the propulsion capabilities of the craft - that is the limiting factor rather than the ability of people to move about on the surface. The lack of substantial gravity would actually impede human locomotion and ability to work on the surface. Any small asteroid mining would be more likely done by small robots rather than clumsy humans, who might easily launch themselves off the surface.

$\endgroup$
4
  • $\begingroup$ Thanks for the video on these upgraded suits, work in progress as you say, but great for space tourism. For asteroids, according to this map nearest asteroid orbits are twice the distance to the Moon (apart from Apophis which will come at 10% Moon distance In 2029). If capsule can match the asteroid speed, it could then dock with it, so we need something moving close to the same speed as Dragon, close by, so we could stay there for one full orbit, then detach and return to Earth. techexplorist.com/… $\endgroup$
    – estinamir
    Commented May 12 at 23:53
  • 6
    $\begingroup$ @estinamir you’re radically underestimating the delta-v requirements for a rendezvous & return mission $\endgroup$ Commented May 13 at 0:12
  • $\begingroup$ I am just trying to simplify it by thinking in terms of docking with ISS which could be similar in size and speed to the asteroid. $\endgroup$
    – estinamir
    Commented May 13 at 0:43
  • 7
    $\begingroup$ @estinamir if an asteroid had a similar speed to the ISS, it would be orbiting in a similar location to the ISS. As-is, most asteroids have a pretty significant delta-v requirement to reach from LEO - AKA a significant difference in performance even after reaching the ISS. Returning will require additional delta-v (presumably you do want to avoid abandoning your astronauts) $\endgroup$ Commented May 13 at 5:58
6
$\begingroup$

Michael MacAskill's answer has talked of limitations of Dragon and the SpaceX space suits, but there is a separate issue with achieving intercept.

Near Earth Objects have broadly similar orbits to earth so achieving a transfer to one from earth escape velocity is low delta V. The key part is that you must achieve escape velocity first, which is less than it took from earth surface to ISS orbit but not by much (3kms LEO to escape vs 9kms surface to LEO). Dragon and similar capsules have hundreds of meters per second DV left once in LEO, not kilometers.

If we go 'aha, I will wait till one of these objects is near earth' we run into the issue that this object will have been accelerated as it comes in towards earth and be moving faster, so we still need system escape velocities on our rocket and now have the problem that our visit time is in minutes or possibly hours if we do not want to spend years on the thing.

The last point is because NEO are actually tricky to do return trips to because their orbits are so similar to earth. If we do a manned mission to an NEO in a 1.2 year orbit at closest approach, it will be five years until next close approach, and early return will involve a very non optimal trajectory. In some ways Mars is easier since return windows happen more often.

What Dragon and similar capsules certainly are capable of is intercepting a NEO as it happens to pass near Earth for a flyby. The issue, and reason it has not been attempted is that the relative velocities will be so high (capsule slow at peak of a lofted orbit, asteroid having accelerated during approach to Earth) that the relative velocities will be at least 3 kilometers a second so humans would not see anything beyond maybe a blur, and digital sensors not doing much better.

What may be more relevant is seeking 'mini moons' objects which will have an interaction with the moon that does a reverse gravity assist and places them on chaotic orbits in the Earth/Moon system. These would be reachable by any vehicle capable of doing a moon mission and allow potentially a couple of weeks or months on site before having to return due impending ejection or collision.

Issue here is that this type of object is rare, random and small (meters), meaning the a mission would have to be prepped and kept on standby, potentially for years until one large enough to justify the trip was detected early enough to allow mission to execute.

$\endgroup$
3
  • 1
    $\begingroup$ Thanks. I may have underestimated that too, thinking it would be as easy as docking with ISS. The mini moons of 500k diameter sounds great. But what about micro asteroids like 50m size (or starship size) or less? They’ve got to be lurking out there, beyond the Moon. So if you could get close buy in a Dragon and harpoon or lasso it, it wouldn’t have a tonne of momentum, so may be you could bring it down to your own speed and then dock. $\endgroup$
    – estinamir
    Commented May 13 at 15:50
  • $\begingroup$ FWIW, Apophis (currently) has a period of ~323.63 days, so its synodic period is ~2840 days (~7.775 years). $\endgroup$
    – PM 2Ring
    Commented May 14 at 8:08
  • 2
    $\begingroup$ @estinamir recommend doing some reading on real world asteroids - there are only a couple of asteroids larger than 100km, the mini moons referenced were mostly sub 20 meter sizes. Though mass is the cube of the size, so a 10*10*10 meter object will still be over 1000 tonnes if solid, so momentum transfer will be the wrong way if you just try to grab on. And while slow be space standards are still traveling at bullet speeds relative to an approaching craft from earth so rough on any grabbing mechanism space.stackexchange.com/a/14103/26356. $\endgroup$ Commented May 14 at 8:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.