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51 votes
Accepted

Soyuz landing ground detection

Earlier Voskhod models used a retractable metal probe, but it was unreliable, especially in windy conditions. So in Soyuz, as the other answers have pointed out, a gamma-ray source is pointed at the ...
Rikki-Tikki-Tavi's user avatar
48 votes
Accepted

How much more expensive are scientific instruments for space use?

Preface: I am far, far from an expert in space electronics; I don't think I can weigh in on how much these sensors actually are, which is the title question; all I can offer is an uneducated inane ...
0xDBFB7's user avatar
  • 2,239
44 votes

Why were contact sensors put on three of the Lunar Module's four legs? Did they ever bend and stick out sideways?

Some pictures from Apollo 11 of the landing gear – struts, footpads and contact probes. Three Apollo 12 images: Two Apollo 14 footpad images: An Apollo 16 image: The two probes bend straight up on ...
Uwe's user avatar
  • 48.9k
41 votes

Soyuz landing ground detection

Soyuz uses gamma rays altimeter "Cactus", which starts soft landing engines just 1 meter before ground. Translation from russian wikipedia: The altimeter uses a source of gamma radiation (usually -...
Pavel Bernshtam's user avatar
39 votes
Accepted

Why were contact sensors put on three of the Lunar Module's four legs? Did they ever bend and stick out sideways?

It is correct that the probe on the forward footpad was omitted to avoid interfering with the ladder: The probe located on the forward landing gear was deleted because of a concern that the failed ...
DrSheldon's user avatar
  • 47.9k
29 votes

How much more expensive are scientific instruments for space use?

I'll chime in with the other two well-stated answers. In addition to all the testing, there is the issue of "What do you do when the instrument fails a test?" Most COTS (Commercial Off-The-Shelf) ...
Tom Spilker's user avatar
  • 18.3k
20 votes

Soyuz landing ground detection

Just to add a better source: From the Soyuz Crew Operations Manual The АКСП consists of barostatic and time mechanisms and the Гамма-лучевой высотомер (ГЛВ) (Gamma Ray Altimeter). The barostatic ...
Organic Marble's user avatar
17 votes
Accepted

Which of the outer planets could you see with the naked eye if you were in close proximity?

You can try for yourself how bright it is on Pluto. High noon on Pluto is as bright as a certain point during dusk/dawn on Earth. I tried this, at that point it's bright enough to make out details. My ...
Hobbes's user avatar
  • 127k
16 votes

Why are the JWST A3 and A6 position sensors different from all the others?

See 2018 SPIE paper by Wolf et al. "JWST mirror and actuator performance at cryo-vacuum" (find it by searching on "JWST A3 and A6 position sensors"). See sec 1.2 and 2.4.2 of the ...
Richard Flasck's user avatar
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. "....
Organic Marble's user avatar
10 votes
Accepted

What sensors or combination of sensors do rockets use during takeoff for their orientation?

As a real-world example, the Space Shuttle used a combination of Inertial Measurement Units (IMUs) and Rate Gyro Assemblies (RGAs). The IMUs sensed accelerations and the RGAs measured body rates. ...
Organic Marble's user avatar
10 votes

How much more expensive are scientific instruments for space use?

Just to give you an idea, here is how the cost might break down. The COTS version will need to be torn apart to survive vibration testing, along with added material. It will need to have some kind of ...
PearsonArtPhoto's user avatar
  • 121k
9 votes

How much more expensive are scientific instruments for space use?

A "one to a million" price factor is not too crazy if you think about it : your pocket thermometer was probably manufactured in over a million copies. The space thermometer is made only once ...
jeancallisti's user avatar
9 votes

Can we detect the projected ISS shadow on the earth surface?

TL;DR; Yes! Use a Raspberry Pi, a square millimeter photodiode, a low cost ADC and some DC and high frequency rejection with a quad op-amp and passive components. Best possible case the ISS presents ...
uhoh's user avatar
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9 votes
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Why were some early interplanetary probes pressurized?

This was done to simplify thermal management. In a pressurized container, you can use air cooling. In a vacuum, you have to use heat pipes or liquid cooling to transfer heat to a radiator. This also ...
Hobbes's user avatar
  • 127k
8 votes

Which of the outer planets could you see with the naked eye if you were in close proximity?

Bright sun light of a clear sky is about 100,000 Lux, room light at night about 100 Lux, street light at night about 10 Lux. We are thus able to see with 1/10000 of the brigthness of summer day with ...
Uwe's user avatar
  • 48.9k
8 votes

Soyuz landing ground detection

They use Cesium-137, which produces low-level radiation, for the landing altimeter. Soyuz hazards (spaceref.com PDF)
Antzi's user avatar
  • 12.7k
8 votes

How is altitude measured in self-landing rocket stages?

The Apollo LM was developed with a self-landing capability in its software, though in practice the mission commander took over manual control at around 150 meters altitude in all the actual landings. ...
Russell Borogove's user avatar
8 votes
Accepted

How fast are Ingenuity's knees wearing out?

Let me open by saying I do not have an answer. Thanks BrendanLuke15 for linking to the knee detail image!! While question is more "design/engineering" than "space exploration"... ...
BradV's user avatar
  • 3,162
7 votes

How much more expensive are scientific instruments for space use?

One more factor that nobody has touched on so far. Here on Earth we aren't too concerned with power use on most instruments. Power's cheap, rarely is it worthwhile to do much to lower the power ...
Loren Pechtel's user avatar
7 votes

Why were contact sensors put on three of the Lunar Module's four legs? Did they ever bend and stick out sideways?

According to W. David Woods' excellent "How Apollo Flew to the Moon", p. 262: Originally a probe had been attached to all four footpads but Neil Armstrong had pointed out the possibility that his ...
stevek_mcc's user avatar
6 votes
Accepted

Gravity Model measurement technique

Since the gravity field is the vector gradient of the gravitational potential field, precise measurements of a spacecraft's trajectory in 3 dimensions and time provide a good sample of that gravity ...
Tom Spilker's user avatar
  • 18.3k
6 votes

Generally, what types of sensors are used in rocket guidance systems?

Traditionally, just an inertial measurement unit. More recently GPS has come into play as an additional sensor to better nail down the state. Yes, a great deal of processing takes place to convert ...
Mark Adler's user avatar
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6 votes
Accepted

Apollo Cross Pointer Working

Both horizontal and lateral velocity could be displayed on the cross-pointer display. Based on the position of the Mode Select and Rate/Err Mon switches, the velocity displayed came from one of ...
Organic Marble's user avatar
5 votes

Spacecraft Horizon Sensors for Lunar orbit

At the temperatures of the lunar surface IR limb sensors would work just fine. (See the post by @BobJacobsen) The problem with a UV sensor is that it requires reflected UV. Relatively little UV energy ...
Tom Spilker's user avatar
  • 18.3k
5 votes

Avoiding rocks when landing on Mars

For a modern autonomous lander, a mix of sensor types will likely be used, but for rock-avoidance, I think LIDAR and optical scanning is probably the most important. Modern computing techniques can ...
Russell Borogove's user avatar
5 votes
Accepted

Remaining fuel estimation/measuring Strategy in a spacecraft

In order to compute for the amount of throttle required the guidance needs mass and inertia (for RCS) of the spacecraft. What's actually important is to know your position, velocity, and acceleration....
Russell Borogove's user avatar
5 votes

Attitude determination during launch and landing

If you want a historical answer, the space shuttle used its Inertial Measurement Units (IMUs) and Rate Gyro Assemblies (RGAs) to determine attitude during ascent. The function of the attitude ...
Organic Marble's user avatar
5 votes

Attitude determination during launch and landing

Another good @OrganicMarble answer to this question is What sensors or combination of sensors do rockets use during takeoff for their orientation? Adding my own experience with other systems, star ...
Ryan C's user avatar
  • 7,852
4 votes

Can we detect the projected ISS shadow on the earth surface?

In terms of detecting the shadow there are a few lengthy answers to, essentially, the same question in reddit. The most concise answer being that the ISS is too small to cast a shadow on the surface ...
aarribas's user avatar
  • 101

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