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54 votes
Accepted

How did the Apollo 11's Eagle ascent stage find the CSM after leaving the Moon?

The process was a great deal more sophisticated than pointing and thrusting, and the CSM was cooking along at over 1600 m/s, circling the moon every 2 hours. Mission control, however, had fairly ...
Russell Borogove's user avatar
40 votes
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Given small computational resources, how was navigation implemented? (Not samples of old guidance software)

In many of the early probes, up until close to Apollo there were not true computers on space probes. All computing was done on Earth and the onboard electronics was known as a sequencer, for Pioneer ...
GremlinWranger's user avatar
33 votes
Accepted

How did astronauts using rovers tell direction without compasses on the Moon?

The Lunar Roving Vehicle did have a (form of) compass. It was gyroscopic rather than magnetic, thus it needed calibration when first powered up using the sun angle as a reference. It's in the upper ...
Russell Borogove's user avatar
28 votes

How will DART be able to hit a 170 meter rock dead-center at over 6000 m/s? What technologies will be use and how will they work together?

Didymos will be roughly 11 million kilometers (6.8 million miles) from Earth at the time of the DART impact.The round trip time for a radio signal from DART to the control center on Earth will be ...
Uwe's user avatar
  • 49k
27 votes

Given small computational resources, how was navigation implemented? (Not samples of old guidance software)

(originally answered to "Samples of old guidance software") The first that comes to mind is the Github repository of the Apollo 11 Guidance Computer (AGC). The repository has both Command Module and ...
Ludo's user avatar
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26 votes
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Lunar Terrain Model in Apollo Guidance Computer

It was very simple. Five sloped straight lines. The terrain is modeled by a series of line segments leading to the nominal landing site. Each line segment is defined by a pair of single-precision ...
Organic Marble's user avatar
25 votes

How would blockchain be integrated into spaceflight? Have any methods been proposed yet?

Blockchain is a very poor solution to a specific problem: achieving ledger consensus among a large number of agents when there is substantial incentive to corrupt the record, and the entries in the ...
Russell Borogove's user avatar
22 votes
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Radar altimeter in a space shuttle

The radar altimeter was intended only for landing, to provide a direct, precise measurement of the altitude of the vehicle above the runway. It locked on around 5000 feet altitude but was primarily ...
Organic Marble's user avatar
21 votes
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How does a space vehicle which carries Curiosity or Spirit rover reach a planet?

Movies are misleading. Space is enormous, and almost entirely empty. Even our ”asteroid belt” is mostly empty space; we have flown several missions straight through the belt to the planets beyond ...
Russell Borogove's user avatar
19 votes

Most accurate attitude determination system in spacecraft?

TL;DR Star trackers are by far the most precise. Sun sensors are used for coarse knowledge and IMUs only for estimating the attitude during a maneuver. Details Attitude determination typically relies ...
ChrisR's user avatar
  • 6,220
16 votes
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What was the globe instrument in Vostok 1?

From russian wikipedia: Another instrument helped to the pilot to decide when to start manual operation to return to Earth - it was a small globe with a clock mechanism, which shows the (calculated, ...
Pavel Bernshtam's user avatar
16 votes

How did astronauts using rovers tell direction without compasses on the Moon?

The rovers used a gyroscope-based navigation system. The Lunar Roving Vehicle (LRV) navigation system consists of a directional gyro, a set of incremental odometers, and a hybrid analog-digital ...
Organic Marble's user avatar
15 votes

Given small computational resources, how was navigation implemented? (Not samples of old guidance software)

I am a software developer and with all the resources available today I cannot fathom where one could even start such an endeavour. There are plenty of computer-based systems to this day that have to ...
David Hammen's user avatar
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15 votes
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Which is more accurate, a Saturn V IU or an iPhone?

The ST-124-M3 platform wins, hands down. The ST-124 was flight tested on the Saturn I flights. I found the corresponding test report "SATURN I BLOCK II GUIDANCE SUMMARY REPORT" from February ...
Ludo's user avatar
  • 14.4k
13 votes
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How are GPS satellite clocks synchronized with each other in the earth's frame of reference?

The satellites' location is very accurately determined using ranging techniques, where a pulse is sent from a ground station to the satellite and the satellite responds very quickly, with a known time ...
PearsonArtPhoto's user avatar
  • 121k
13 votes
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How might Earth's location be referenced in stellar terms?

Like the lower left part of the image below. Define a set of pulsars through describing proportions between their frequencies. Define distances from each of them. This uniquely identifies a point in ...
SF.'s user avatar
  • 55k
13 votes
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When did Houston figure out where the Eagle had landed?

They used the rendezvous radar on the LM to pinpoint the CSM's relative direction, and worked backwards from that info and the CSM's location in order to pinpoint the LM. Here's the commentary from ...
Russell Borogove's user avatar
12 votes

Height of navigation satellites above Earth

For satellite navigation, you are most likely using the Global Positioning System, which uses six planes of satellites at an altitude of 20,180 km. However, many systems can also use the GLONASS ...
SE - stop firing the good guys's user avatar
12 votes

Spacecraft Navigation

Navigation to high accuracy is done using radiometric tracking. There are scads of references, such as here, here (don't let the Russian language on the title slide scare you off!), and here, that ...
Tom Spilker's user avatar
  • 18.3k
12 votes
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How would the state vector be updated in the Apollo Guidance Computer during coasting to/from the moon if communication with Earth was lost entirely?

The restrictions you are quoting only apply to the LGC, the computer in the Lunar Module. The Command Module Computer does not have these restrictions (compare the section about the Coasting ...
indy91's user avatar
  • 1,991
12 votes
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Perseverance Rover to drive carefully for months while helicopter hangs from underside?

The helicopter and the deployment assembly are protected by a "debris shield" which is only dropped shortly before helicopter deployment. This shield is formed out of carbon fiber and fully ...
Dragongeek's user avatar
  • 18.8k
11 votes
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A gedanken on being able to navigate back to Earth

Answering the corrected question, "I was interested in if we could look at the stars and constellations in the sky to get back to earth. So assume navigation only by looking at the space." The answer ...
Mark Olson's user avatar
11 votes

Perseverance Rover to drive carefully for months while helicopter hangs from underside?

No, Perseverance will not drive for months with the helicopter stowed on its underside. From the Surface Phase of the Mars 2020 Perseverance Launch Press Kit I got the information below. The first 30 ...
Cornelis's user avatar
  • 7,545
10 votes

How does GPS work exactly?

Does the receiver calculate the distance that separates it from each satellite, or does it just calculate the distance difference between each pair of satellites? A basic answer is a global ...
mins's user avatar
  • 5,033
10 votes
Accepted

How is space mapped out?

There are many different coordinate systems (X, Y, Z axes as you refer to them). The center of the Earth is often used as the origin "center" of the coordinate system, at least for calculations ...
Organic Marble's user avatar
10 votes
Accepted

Machine Learning and Classical Navigation, Guidance and Control in Space Exploration

This is an attempt at the first part of your question: "are classical control algorithms better than machine learning approaches". Since I am personally more interested in launch vehicles, the answer ...
Przemek D's user avatar
  • 375
10 votes

Is it possible to navigate space travel with no computer?

You can travel in space without any navigation devices or computers at all, establishing suborbital flight and orbital flight is done by the rocket, it's accuracy there that matters and early manned ...
GdD's user avatar
  • 20.3k
10 votes

Is there any kind of research on *sub*-orbital rendezvous-ing with a space tug outside the atmosphere?

I can't find anything on this online. It would seem to be a useful technique as it would lower the delta-v for the vehicle that lifts the payload from the ground to the rendezvous point relative to ...
Russell Borogove's user avatar
10 votes
Accepted

How did the star tracker on the Corona (Key Hole) satellite work?

I think, though I'm not certain, that Wikipedia is in fact wrong in this situation, probably for the reason you just mentioned. From this article, A square peg in a cone-shaped hole: The Samos E-5 ...
Starfish Prime's user avatar
10 votes

Modeling attitude control: ramping/easing between attitude commands?

A naive bang-bang approach can consume excessive amounts of propellant when the vehicle needs to achieve large changes in attitude. The rotation rate can get excessively large at the switchover point. ...
David Hammen's user avatar
  • 74.8k

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