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It looks from the videos that the boosters return to land using strictly thrust from the rocket. Can someone explain why it's done that way and a parachute isn

It looks from the videos that the boosters return to land using strictly thrust from the rocket. Can someone explain why it's done that way and a parachute isn't used for at least part of the descent? Seems like an awful waste of fuel.

sfeng 10y ago
The answer is the same as why the Falcon 9 uses propulsive landing. Parachutes are heavy, and generally require a water landing which seriously damages the booster (not to mention requires a recovery operation). The vast majority of the weight in these spacecraft is fuel, so when it's time for it to return to the pad it requires a comparatively small amount of fuel (as most of the weight has been burnt up). The fuel itself is also a tiny percentage of the total cost of the craft, at interplanetary scale $10k for a little extra fuel is nothing.
jessriedel 10y ago
> SpaceX experimented with using parachutes in the past (mainly for their Falcon 1 vehicles), but parachutes are poorly suited to this application, as extreme speeds and loads cause them to shred. Parachutes large enough to recover the stage are also quite heavy, a weight which could be used for fuel for a propulsive landing and for primary mission assurance. Parachutes also cannot be steered. > Essentially, this becomes a problem of people overestimating the amount of fuel required to bring the stage back, underestimating the weight of the parachute system (which would be in the hundreds of kilograms at least), and underestimating the fragility and controllability of a parachute system. https://www.reddit.com/r/spacex/wiki/faq/reusability https://www.reddit.com/r/spacex/wiki/faq/reusability
extrapickles 10y ago
Parachutes put large loads on the structure when opening and don't have much precision in choosing a landing site.
rtkwe 10y ago
Part of it is that there's not a good middle area for them to work. F9 has to use rockets at the beginning for the boost back burn in space and would need to use it again around landing because parachutes aren't gentle or controlled/precise enough for a landing on land or a barge.
mikeash 10y ago
Fuel is cheap, and the parachutes you'd need to soft-land a rocket like this would be gigantic. The weight and cost of the two systems are more similar than you might realize. Propulsive landing gives you much more control over where you end up.
Animats 10y ago
Because Mars doesn't have a thick enough atmosphere to parachute-land a big spacecraft. The atmosphere is thin not only in density but in altitude. It wasn't until about 15 years ago that it was realized that we had no clue how to land a large craft on Mars. "Plainly put, with our current capabilities, a large, heavy vehicle, streaking through Mars’ thin, volatile atmosphere only has about ninety seconds to slow from Mach 5 to under Mach 1, change and re-orient itself from being a spacecraft to a lander, deploy parachutes to slow down further, then use thrusters to translate to the landing site and finally, gently touch down." - JPL.[1] The approaches used for the small landers don't scale. Giant supersonic parachutes a hundred meters across don't look workable. There are some exotic parachute/heat shield concepts such as "hypercones" which have never been tried. Deceleration outside the atmosphere with rockets takes huge amounts of fuel, but should work. The refueling in orbit plan makes sense. (Sending the fuel tank up first would be simpler, if less impressive visually. Build up fuel storage in orbit with multiple launches. This was von Braun's original lunar plan.) [1] http://www.universetoday.com/7024/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet/# http://www.universetoday.com/7024/the-mars-landing-approach-...
grecy 10y ago
Musk answered that in the talk. Using parachutes limits you to only landing on places that have a thick(ish) atmosphere. Being propulsive, they can land this thing anywhere in the entire solar system. (Then he said Venus would be tricky, and it must be solid, not liquid)

sfeng 10y ago

The answer is the same as why the Falcon 9 uses propulsive landing. Parachutes are heavy, and generally require a water landing which seriously damages the booster (not to mention requires a recovery operation). The vast majority of the weight in these spacecraft is fuel, so when it's time for it to return to the pad it requires a comparatively small amount of fuel (as most of the weight has been burnt up). The fuel itself is also a tiny percentage of the total cost of the craft, at interplanetary scale $10k for a little extra fuel is nothing.

jessriedel 10y ago

> SpaceX experimented with using parachutes in the past (mainly for their Falcon 1 vehicles), but parachutes are poorly suited to this application, as extreme speeds and loads cause them to shred. Parachutes large enough to recover the stage are also quite heavy, a weight which could be used for fuel for a propulsive landing and for primary mission assurance. Parachutes also cannot be steered. > Essentially, this becomes a problem of people overestimating the amount of fuel required to bring the stage back, underestimating the weight of the parachute system (which would be in the hundreds of kilograms at least), and underestimating the fragility and controllability of a parachute system. https://www.reddit.com/r/spacex/wiki/faq/reusability https://www.reddit.com/r/spacex/wiki/faq/reusability

extrapickles 10y ago

Parachutes put large loads on the structure when opening and don't have much precision in choosing a landing site.

rtkwe 10y ago

Part of it is that there's not a good middle area for them to work. F9 has to use rockets at the beginning for the boost back burn in space and would need to use it again around landing because parachutes aren't gentle or controlled/precise enough for a landing on land or a barge.

mikeash 10y ago

Fuel is cheap, and the parachutes you'd need to soft-land a rocket like this would be gigantic. The weight and cost of the two systems are more similar than you might realize. Propulsive landing gives you much more control over where you end up.

Animats 10y ago

Because Mars doesn't have a thick enough atmosphere to parachute-land a big spacecraft. The atmosphere is thin not only in density but in altitude. It wasn't until about 15 years ago that it was realized that we had no clue how to land a large craft on Mars. "Plainly put, with our current capabilities, a large, heavy vehicle, streaking through Mars’ thin, volatile atmosphere only has about ninety seconds to slow from Mach 5 to under Mach 1, change and re-orient itself from being a spacecraft to a lander, deploy parachutes to slow down further, then use thrusters to translate to the landing site and finally, gently touch down." - JPL.[1] The approaches used for the small landers don't scale. Giant supersonic parachutes a hundred meters across don't look workable. There are some exotic parachute/heat shield concepts such as "hypercones" which have never been tried. Deceleration outside the atmosphere with rockets takes huge amounts of fuel, but should work. The refueling in orbit plan makes sense. (Sending the fuel tank up first would be simpler, if less impressive visually. Build up fuel storage in orbit with multiple launches. This was von Braun's original lunar plan.) [1] http://www.universetoday.com/7024/the-mars-landing-approach-getting-large-payloads-to-the-surface-of-the-red-planet/# http://www.universetoday.com/7024/the-mars-landing-approach-...

grecy 10y ago

Musk answered that in the talk. Using parachutes limits you to only landing on places that have a thick(ish) atmosphere. Being propulsive, they can land this thing anywhere in the entire solar system. (Then he said Venus would be tricky, and it must be solid, not liquid)