90
votes
Accepted
Why was it necessary to program InSight with an ability to land in dust storms?
Because it's at the end of a 6 month cruise and there's no turning back.
InSight will not enter closed orbit around Mars - its trajectory is hyperbolic so either it misses Mars entirely or it enters ...
- 9,904
56
votes
Accepted
What is a "suicide burn"?
For a powered descent to the surface of a massive body like the Moon, it turns out to be most fuel efficient to do all your deceleration at the very end of the trajectory, right before impact.
(This ...
- 165k
32
votes
Why was it necessary to program InSight with an ability to land in dust storms?
InSight doesn't enter Martian orbit before EDL; it plows straight into Mars' atmosphere from interplanetary space. Thus, the time of landing is pretty much un-alterable after its final midcourse ...
- 165k
27
votes
Accepted
Why is InSight's nylon parachute a "soft good"?
I'm pretty sure that by "soft good" he means it's an element of the system that can't be completely constrained from a simulation or engineering standpoint, in this case fabric. If you're working with ...
- 16.7k
23
votes
Accepted
How did NASA avoid a repeat of the Mars Polar Lander failure?
The failure analysis report includes a large laundry list of recommendations to prevent a repeat failure. As usual in these reports, corrective actions are listed for potential causes that were found ...
- 174k
22
votes
Why won't NASA show any computer screens?
A long, long time ago, I managed to arrange to get two passes to see the first light from one of the Voyager flybys of Jupiter. I collected on lots of debts and pulled lots of strings to get those ...
- 71.8k
21
votes
Is there a risk that re-entering capsules or other components will hit ships or islands?
Partial Answer:
From Apollo by the Numbers we can see that even in the 1960s and 1970s the splashdown point was quite predictable.
Page 305 shows the maximum miss distance to the target point was 3 ...
- 174k
17
votes
Accepted
When things land on Mars what fraction of their velocity do they remove propulsively?
Taking Mars Pathfinder and Viking 1 as examples:
Mars Pathfinder was a direct entry at 7600 m/s and removed about 0.7-0.8% of that propulsively. Parachute deployment was at 360-450 m/s, and landing ...
- 9,867
16
votes
How does a Mars lander reach a chosen landing site?
There are typically five planned trajectory correction maneuvers on the way to Mars, referred to as TCM-1 to TCM-5. (Also there is a slot for an emergency TCM-6 a few hours before entry, but it is not ...
- 58.3k
16
votes
Why don't SpaceX boosters belly flop?
Think about heat and air resistance.
The falcon 9 has no heat shield on its side and Starship does, so making the falcon 9 booster reenter sideways could break it.
Also the amount of drag at such high ...
- 4,272
15
votes
Curiosity and Perseverance landing - with so much dust blown everywhere, what's the point of the skycrane?
because it would prevent the rockets from contaminating the landing site.
No they weren't
There was some possible advantage from that, to be sure. But missions to Mars undergo serious levels of ...
- 1,920
13
votes
Accepted
What happens to Insight's parachute on Mars?
I'm pretty sure it will be like the Phoenix lander. Collectively that part of the lander is referred to as the "Backshell". This is the image of Phoenix of the hardware on the surface.
This is ...
- 121k
12
votes
Accepted
How does a gamma ray altimeter work? What kind of sensor is used?
It's called the "Kaktus-2".
The sensor is referred to as a "NaI(TI) crystal detector" which appears to be a scintillation counter.
The device has a 2 of 3 voting scheme to avoid false positives.
"....
- 174k
12
votes
Is there a risk that re-entering capsules or other components will hit ships or islands?
Partial answer:
According to russianspaceweb.com, there are a set of large, pre-selected landing sites for the Soyuz capsules.
Soyuz can land with an accuracy of only 28 kilometers, (with a ...
- 932
11
votes
Accepted
Why does in-flight mission abort often ends in ballistic high-g reentry?
When you're in orbit you have velocity roughly parallel to the atmosphere, a flat-ish shape angled properly can "fly" across it in a lifting entry where you can dissipate energy in the thinner upper ...
- 19.2k
11
votes
What happens to Insight's parachute on Mars?
During the parachute descent, InSight's trajectory is at an angle to the vertical. After the backshell and parachute separate, the engines fire, leveling the craft. This allows some horizontal ...
- 47.4k
11
votes
Why are cone shaped heat shields used for Mars entry?
The following paragraph, in section IIIF of Prabhu and Saunders On Heatshield Shapes for Mars Entry Capsules, is the only direct comparison between 70-degree cones (Mars Viking heritage) and spherical ...
- 9,025
10
votes
Can a blimp dead drop on Mars or Earth this way?
NASA is working on an inflatable heat shield. Not quite a blimp, but a heat shield that's inflatable to a size much larger than the probe it's attached to. The extra area helps decelerate the ...
- 123k
9
votes
Accepted
Blimp on Earth, but a glider on Mars?
Unfortunately my answer won't contain the crucial "yes" or "no" - for the simple reason that one hinges upon fine parameters and would likely require a good NASA study for actual answer. But the ...
- 54.3k
9
votes
Accepted
Archimedean braking for low density Venus lander + subsidiary question
Surprisingly the answer is yes there was studies done on that subject.
A simple google search could yield this result:
BUOYANT PLANETARY ENTRY
https://apps.dtic.mil/dtic/tr/fulltext/u2/642361.pdf
...
- 12.6k
9
votes
Accepted
What is crossrange and downrange for an entry vehicle?
Downrange is the distance traveled in the direction of flight. Imagine the orbit of a spacecraft as a circle around the Earth, 'downrange' is the distance traveled along this path. When you do a ...
- 123k
9
votes
Accepted
How long does the descent of the Falcon 9 first stage take?
It will vary somewhat mission-to-mission, but it's generally about 6 minutes from separation to first-stage touchdown. It's not very different between LEO and GEO missions, as the first stage only ...
- 165k
9
votes
Is there a risk that re-entering capsules or other components will hit ships or islands?
The first of your several questions is about controlled reentry of devices designed for reentry. You then ask about devices not designed for reentry, which I address (partially).
Undesigned reentry ...
- 191
9
votes
Why won't NASA show any computer screens?
In trying to explain my feelings on this question in comments on the other answer, I came around to a possible explanation -- There could be a real PR cost to publishing raw data streams in real time.
...
- 6,407
8
votes
How different was the Apollo LM descent trajectory from the most fuel-efficient?
The limiting case assumes a perfectly spherical moon and a lander that can do instantaneous burns of any magnitude.
In this case, starting from a 110km circular orbit, the lander does a brief burn ...
- 165k
8
votes
Accepted
Meteor color hints at chemistry
Absolutely, it's the same as heating up metals with a blowtorch. The colour of the flame tells you what is present. Wikipedia actually has a handy list giving an indication of the significant elements ...
- 13.6k
8
votes
Accepted
Can we significantly reduce entry velocity with this method by airbraking alone for interplanetary travel?
You can use skip reentry to gradually reduce your speed when arriving from an interplanetary journey. NASA also studies skip reentry for the Shuttle, as a way to reduce the heat load during reentry. ...
- 123k
8
votes
Why was it necessary to program InSight with an ability to land in dust storms?
To deal with dust storms, two of the changes between Phoenix and InSight are mechanical in nature:
InSight uses a thicker heat shield, partly to handle the possibility of being sandblasted by a ...
- 47.4k
8
votes
Accepted
Why Crew Dragon needs 18 hours between ISS separation and descent?
There are a few necessary activities and schedule considerations that contributed to needing 18 hours between undock and entry.
Sleep
Loading the Crew Dragon with returning (“down-mass”) gear, ...
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