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> They need to be able to stabilize the rocket's landing in all sorts of conditions if they want to have any hope of landing it on another planet. Well, not re

by daeken 12y ago

> They need to be able to stabilize the rocket's landing in all sorts of conditions if they want to have any hope of landing it on another planet. Well, not really. Dragons (and Red Dragons, for interplanetary travel) are way, way less sensitive to the whims of weather. The issue with the first stage is that you have a very large, very fragile, very bottom-heavy tin can that you're trying to balance on a moving platform. This is entirely different than trying to land a pod, which is what we'll be doing on other planets. Dragon v2 will be landing on land (though doing parachute recovery from water for initial CCS missions, as per NASA spec), and we'll see how stable it is then.

deleted 12y ago
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- segacontroller 12y ago
  OK that may be the long term goal, but what is the short term goal? What is the goal of landing this rocket stage on earth? Is it to use this model to land on another planet, or is it to use this model to reduce costs and reuse the first stage of the rocket?
  - deleted 12y ago
    [deleted]
  - _broody 12y ago
    It's the later. Every other possible use of the technology is just speculation at this point.
  - TeMPOraL 12y ago
    Short term and primary goal? Significantly cut down the costs of access to space. But long term goal is landing and taking off from another worlds, and this project produces important engineering insights that may prove useful for that goal. SpaceX has a habit of hitting multiple targets at once.
- daeken 12y ago
  As far as I'm aware, there's no plan for rocket refueling on Mars. That makes sense, considering that the stages we normally think of as the 'rocket' will be gone long before our pods get to Mars. We will refuel the pod, which has its own rocket engines on it, and use that to get back up (with a tiny fraction of the original payload) from the surface. Mars' gravity well and atmosphere are a fraction of Earth's, so there's really no need for a multi-stage rocket and all that. A refueled and weight reduced pod will do it just fine.
  - lotsofmangos 12y ago
    You could probably put a rocket stage capable of a Mars landing and then takeoff after refueling on top of a stage capable of an Earth landing. I think this is being looked at, as though the gravity well is smaller than Earth's, it is not small enough for a crewed pod ascent like the moon landing. From my understanding this is one of the reasons other than looking for life to want easy to access water, as then you can make rocket fuel with solar panels.
    - el_zorro 12y ago
      Mars would almost certainly require a small rocket to get to orbit, but it would be trivially sized compared to what we need on Earth. Even something as small as the Atlas rockets that brought the first Americans to space would probably be overpowered compared to Mars' small gravity well. Throw in atmospheric losses less than a hundredth of that on Earth and suddenly space becomes very accessible.
Cshelton 12y ago
On top of that, they are trying to do it with the main engines, combined with the light weight of the almost empty stage..the power can only be reduced so much. They can't hover and stabilize. They literally have to have a landing burn that makes the velocity at height 0... = 0. Which is incredibly hard enough on stable ground, even more on water. Maybe they'll figure out how to cut off engines as the stage slows down so that the acceleration change isn't so drastic and it could actually have a miniature 'abort' land. Where it would go back up slightly to re position itself in the event of weather, wind, rough waters, etc.
- lmm 12y ago
  > Which is incredibly hard enough on stable ground, even more on water. I dunno, my Kerbal Space Program experience is that water at least doesn't have mountains to crash into.
grecy 12y ago
If Dragon lands on some other planet, how does it get back without a stage 1 also landing on said planet?
- daeken 12y ago
  It's refueled in-situ and launched back up with a minimal payload weight. Getting off the surface of Mars back into an orbit with a low weight (basically crew + life support + minimal payload) is pretty straightforward, considering the low gravity and thin atmosphere. From there, you can dock to a much larger tug ship and go back to Earth orbit, refueling on orbit and landing propulsively again.
  - toomuchtodo 12y ago
    I didn't spend the time searching google to provide citations, but it is feasible to generate fuel autonomously on the Martian surface and store it for future use. Can we launch a vehicle that will de-orbit, safely land, and then begin processing fuel using nuclear (edit: I removed solar here; solar would not provide enough power for such a facility) for power and the Martian atmosphere and soil as feedstock? Not quite yet, but we're getting there.
    - el_zorro 12y ago
      I don't think it is so much an issue of ability so much as desire. Most of the tech has been dreamed up for decades, but it needs funding and a green light (particularly the nuclear reactor, given that there were protests about even Curiosity's RTG). Personally, I think there's a huge amount of talent just waiting for the right moment to strike, and then the whole Mars thing is going to burst right open.
    - danielweber 12y ago
      I believe solar would work, but it would just take longer. EDL for a substantial payload to Mars hasn't been done before, but there's no reason to think it's a show-stopper. A lot of the engineering challenges for that are the same as the engineering challenges for returning the first-stage to Earth, like supersonic retrorockets.

by daeken 12y ago

deleted 12y ago

[deleted]

segacontroller 12y ago
OK that may be the long term goal, but what is the short term goal? What is the goal of landing this rocket stage on earth? Is it to use this model to land on another planet, or is it to use this model to reduce costs and reuse the first stage of the rocket?
- deleted 12y ago
  [deleted]
- _broody 12y ago
  It's the later. Every other possible use of the technology is just speculation at this point.
- TeMPOraL 12y ago
  Short term and primary goal? Significantly cut down the costs of access to space. But long term goal is landing and taking off from another worlds, and this project produces important engineering insights that may prove useful for that goal. SpaceX has a habit of hitting multiple targets at once.
daeken 12y ago
As far as I'm aware, there's no plan for rocket refueling on Mars. That makes sense, considering that the stages we normally think of as the 'rocket' will be gone long before our pods get to Mars. We will refuel the pod, which has its own rocket engines on it, and use that to get back up (with a tiny fraction of the original payload) from the surface. Mars' gravity well and atmosphere are a fraction of Earth's, so there's really no need for a multi-stage rocket and all that. A refueled and weight reduced pod will do it just fine.
- lotsofmangos 12y ago
  You could probably put a rocket stage capable of a Mars landing and then takeoff after refueling on top of a stage capable of an Earth landing. I think this is being looked at, as though the gravity well is smaller than Earth's, it is not small enough for a crewed pod ascent like the moon landing. From my understanding this is one of the reasons other than looking for life to want easy to access water, as then you can make rocket fuel with solar panels.
  - el_zorro 12y ago
    Mars would almost certainly require a small rocket to get to orbit, but it would be trivially sized compared to what we need on Earth. Even something as small as the Atlas rockets that brought the first Americans to space would probably be overpowered compared to Mars' small gravity well. Throw in atmospheric losses less than a hundredth of that on Earth and suddenly space becomes very accessible.

Cshelton 12y ago

On top of that, they are trying to do it with the main engines, combined with the light weight of the almost empty stage..the power can only be reduced so much. They can't hover and stabilize. They literally have to have a landing burn that makes the velocity at height 0... = 0. Which is incredibly hard enough on stable ground, even more on water. Maybe they'll figure out how to cut off engines as the stage slows down so that the acceleration change isn't so drastic and it could actually have a miniature 'abort' land. Where it would go back up slightly to re position itself in the event of weather, wind, rough waters, etc.

lmm 12y ago
> Which is incredibly hard enough on stable ground, even more on water. I dunno, my Kerbal Space Program experience is that water at least doesn't have mountains to crash into.

grecy 12y ago

If Dragon lands on some other planet, how does it get back without a stage 1 also landing on said planet?

daeken 12y ago
It's refueled in-situ and launched back up with a minimal payload weight. Getting off the surface of Mars back into an orbit with a low weight (basically crew + life support + minimal payload) is pretty straightforward, considering the low gravity and thin atmosphere. From there, you can dock to a much larger tug ship and go back to Earth orbit, refueling on orbit and landing propulsively again.
- toomuchtodo 12y ago
  I didn't spend the time searching google to provide citations, but it is feasible to generate fuel autonomously on the Martian surface and store it for future use. Can we launch a vehicle that will de-orbit, safely land, and then begin processing fuel using nuclear (edit: I removed solar here; solar would not provide enough power for such a facility) for power and the Martian atmosphere and soil as feedstock? Not quite yet, but we're getting there.
  - el_zorro 12y ago
    I don't think it is so much an issue of ability so much as desire. Most of the tech has been dreamed up for decades, but it needs funding and a green light (particularly the nuclear reactor, given that there were protests about even Curiosity's RTG). Personally, I think there's a huge amount of talent just waiting for the right moment to strike, and then the whole Mars thing is going to burst right open.
  - danielweber 12y ago
    I believe solar would work, but it would just take longer. EDL for a substantial payload to Mars hasn't been done before, but there's no reason to think it's a show-stopper. A lot of the engineering challenges for that are the same as the engineering challenges for returning the first-stage to Earth, like supersonic retrorockets.