5 ms·

ACKSHULLY - aerobraking on Mars is a chore. The atmosphere is dense enough to burn you to a crisp, thin enough it won't help you slow down - much. Look at the

ACKSHULLY - aerobraking on Mars is a chore. The atmosphere is dense enough to burn you to a crisp, thin enough it won't help you slow down - much. Look at the marvel that is the Skycrane. Not needed for the Moon.

niftich 9y ago
For a dramatic coverage of this exact subject, I highly recommend 'Curiosity's Seven Minutes of Terror' [1] from NASA JPL. [1] https://www.jpl.nasa.gov/video/details.php?id=1090; https://www.jpl.nasa.gov/video/details.php?id=1090; or on Youtube: https://www.youtube.com/watch?v=h2I8AoB1xgU https://www.youtube.com/watch?v=h2I8AoB1xgU
- Robotbeat 9y ago
  Note this is before SpaceX proved supersonic retropropulsion works just fine. Atmosphere is now a huge asset for Mars EDL.
rory096 9y ago
>thin enough it won't help you slow down - much. No. It's thin enough you can't land with parachutes alone. It's still enough that Mars Global Surveyor used it to make up a 1,250 m/s delta-v deficit. Is landing on Mars more complex than a thick atmospheric landing on parachutes or an exoatmospheric landing on propulsion only? Yes. But the atmosphere still saves you a lot of delta-v. [0] https://mars.jpl.nasa.gov/mgs/sci/aerobrake/SFMech.html https://mars.jpl.nasa.gov/mgs/sci/aerobrake/SFMech.html
- keenerd 9y ago
  > It's still enough that Mars Global Surveyor used it to make up a 1,250 m/s delta-v deficit. It took MGS 15 months (not counting delays) of aerobraking to do that. MGS only weighed 1000kg too. Maybe it could work for shipping large, pre-assembled, empty hab modules to Mars before people get there. (Low density, higher drag, no rush.) But not practical for actual human bodies or even resupply since the Hohmann transfer takes a mere 8.5 months. Adding an aerobraking maneuver could easily triple the transit time.
  - simonh 9y ago
    It only took that long because MGS was aerobraking into orbit and wasn't designed to survive the stress of lower atmosphere turbulence, so only used the uppermost layer of the atmosphere for braking. If your going to land, obviously you get to use all the atmosphere and also can use parachutes. Something a problem braking into orbit can't do. Surface probes do direct descent trajectories. There is no extended series of repeated braking passes. You do it in one go.
    - dragonwriter 9y ago
      > If your going to land, obviously you get to use all the atmosphere and also can use parachutes. Something a problem braking into orbit can't do. Also, you can use lithobraking.
      - deleted 9y ago
        [deleted]
      - deleted 9y ago
        [deleted]
Robotbeat 9y ago
7 minutes of terror is a fantastic video, but that line in it always bugged me. Atmosphere is an enormous asset for Sending large payloads to Mars now that we know supersonic retropropulsion works just fine.

niftich 9y ago

For a dramatic coverage of this exact subject, I highly recommend 'Curiosity's Seven Minutes of Terror' [1] from NASA JPL. [1] https://www.jpl.nasa.gov/video/details.php?id=1090; https://www.jpl.nasa.gov/video/details.php?id=1090; or on Youtube: https://www.youtube.com/watch?v=h2I8AoB1xgU https://www.youtube.com/watch?v=h2I8AoB1xgU

Robotbeat 9y ago
Note this is before SpaceX proved supersonic retropropulsion works just fine. Atmosphere is now a huge asset for Mars EDL.

rory096 9y ago

>thin enough it won't help you slow down - much. No. It's thin enough you can't land with parachutes alone. It's still enough that Mars Global Surveyor used it to make up a 1,250 m/s delta-v deficit. Is landing on Mars more complex than a thick atmospheric landing on parachutes or an exoatmospheric landing on propulsion only? Yes. But the atmosphere still saves you a lot of delta-v. [0] https://mars.jpl.nasa.gov/mgs/sci/aerobrake/SFMech.html https://mars.jpl.nasa.gov/mgs/sci/aerobrake/SFMech.html

keenerd 9y ago
> It's still enough that Mars Global Surveyor used it to make up a 1,250 m/s delta-v deficit. It took MGS 15 months (not counting delays) of aerobraking to do that. MGS only weighed 1000kg too. Maybe it could work for shipping large, pre-assembled, empty hab modules to Mars before people get there. (Low density, higher drag, no rush.) But not practical for actual human bodies or even resupply since the Hohmann transfer takes a mere 8.5 months. Adding an aerobraking maneuver could easily triple the transit time.
- simonh 9y ago
  It only took that long because MGS was aerobraking into orbit and wasn't designed to survive the stress of lower atmosphere turbulence, so only used the uppermost layer of the atmosphere for braking. If your going to land, obviously you get to use all the atmosphere and also can use parachutes. Something a problem braking into orbit can't do. Surface probes do direct descent trajectories. There is no extended series of repeated braking passes. You do it in one go.
  - dragonwriter 9y ago
    > If your going to land, obviously you get to use all the atmosphere and also can use parachutes. Something a problem braking into orbit can't do. Also, you can use lithobraking.
    - deleted 9y ago
      [deleted]
    - deleted 9y ago
      [deleted]

Robotbeat 9y ago

7 minutes of terror is a fantastic video, but that line in it always bugged me. Atmosphere is an enormous asset for Sending large payloads to Mars now that we know supersonic retropropulsion works just fine.