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50

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 ground and the backscatter is measured. The instrument ("Kaktus"), was developed in the early 60s. http://www.spacesafetymagazine.com/spaceflight/reentry-...


47

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 ramble on where that money might be going. Let's take your analogy of a bargain-basement thermal sensor; actually, let's specify a common off the shelf Melexis ...


41

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 the left of the left and right footpad. I found no Apollo 17 images with visible contact probes. So yes, some contact probes did bend and stick out sideways. ...


39

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 - Со 60, Сs 137 isotopes). The receiver detects backscattering, reflected from the atoms inside the underlying surface. Gamma ray altimeters are used at low ...


36

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 probe could interfere with crewmen descending the LM ladder. [p. 8] There was more than one probe for redundancy. In particular, there was no electrical ...


28

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) instruments you might get at Home Depot or even Omega Engineering are designed to work in an Earth environment, with some margin. But not too much margin; that ...


19

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 and time mechanisms operating according to their settings issue commands for sequential parachute deployment and for the execution of pre-landing ...


12

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 conclusion is that you can see the daylight side of every planet incl. Pluto with the naked eye if you're close enough. This does depend on the planet's ...


10

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. "...the source emits 13.7 Sv/hr point blank at 1 cm, and 1.3 mSv/hr at one meter. That's quite hot :)" Here's a picture of the device. And here's a block ...


10

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 software written to send the data to the spacecraft. Some testing will need to be done to see if the instrument will work on Mars. The thermal issue will ...


8

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. The IMUs were mounted on a navigation base in the crew compartment. The RGAs were mounted in the midbody, and there were additional RGAs mounted in the Solid ...


8

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 about 3200 square meters of occulting area. Since the solar panels move in various ways, let's also consider half of that, or 1600 square meters. The shortest ...


8

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 explains the failures: as the air leaked out, heat transfer was impaired to the point were components would overheat. As the space race progressed, ...


7

They use Cesium-137, which produces low-level radiation, for the landing altimeter. Soyuz hazards (spaceref.com PDF)


6

A "one to a million" price factor is not too crazy if you think a bout it : your pocket thermometer was probably manufacturered in over a million copies. The space thermomether is made only once (or five times, tops). Hence the cost ratio. Add to that the crazy quality control and the exponential paperwork it implies, and you'll get the picture.


6

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 consumption. On a rocket, though, power either comes from solar cells (and you have to pay to lift them, and the batteries for when they're shielded from the sun) ...


6

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 the data from the sensors into a filtered state, comparing that state to the desired state at that moment in time, and coming up with various commands, kept ...


6

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 descent down the ladder might be impeded by a large length of metal probe that had been bent in some unpredictable way during the landing. The probe below the ...


6

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 four (for lateral velocity) or one of three (for forward velocity) sources. Lateral Velocity: Rate / Err Mon switch in Rndz Radar position: Rendezvous Radar ...


5

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 clear sky. If the distance to the sun is 10 times greater, brightness is 1/100 smaller. Seeing an outer planet in a distance of 100 au to the sun (1 au is the ...


5

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 derive a 3-D model from stereo camera imaging in real time. Strictly speaking, that doesn't distinguish between hard rock and soft soil, but between flat and non-...


4

The generic answer is: rockets use accelerometers, rate sensors (gyros), and/or GPS to measure their position and attitude during flight. Often these are packaged together as an "inertial reference unit" or an "inertial measurement unit". For a more specific answer, you can look at Honeywell's SIGI, which is used by a variety of real-life rockets: It ...


4

In addition to LiDAR and stereo cameras (both work well, cameras are cheaper), you can consider surveying from orbit first and picking a location that is already mostly free of rocks. That's how it's currently done for Mars landers.


4

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. Estimates of mass are obviously useful but don't have to be 100% accurate if you have closed-loop control and good knowledge of your current acceleration. ...


4

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 is emitted from the moon, either by thermal emission or by impacts of natural radiation. This means that if the limb the instrument would see is not ...


4

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 field along the spacecraft's path. Tracking for a long period of time, over a path that covers longitudes and latitudes (so a polar orbit is best for this) gives ...


3

The concentration of an atmospheric constituent is the number of molecules of that chemical species per volume, and that varies with pressure and temperature. In planetary atmospheric science we usually refer instead to abundance, often specifying it by the species's mixing ratio: given a sample of the atmosphere, the fraction of the total number of ...


3

Measure of propellant level in zero-gee tankage is a tricky problem. Shuttle attempted it in its Orbital Manuevering System. A capacitance gauging system in each OMS propellant tank measures the propellant in the tank. The system consists of a forward and aft probe and a totalizer. The forward and aft fuel probes use fuel (which is a conductor) as ...


3

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 of the earth. The earth being in fact in the antumbra of the ISS. On the other hand, we have means of knowing actively where the ISS is. So what would be the ...


3

Is there any history or merit to using a PIR (Pyroelectric ("Passive") InfraRed Sensor) as a sun sensor for determining the attitude or position of a Satellite? I can address the "merit" part to some extent. PIR detectors are more complicated than a simple photodiode for a couple of reasons. They usually are thermopiles and require a "hot" and "cold" side, ...


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