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 ...
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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 ...
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33 votes
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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 ...
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30 votes
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How did astronauts navigate the Lunar Roving Vehicle (LRV) over the surface of the Moon?

The navigation system used a combination of magnetic pickups in the wheels (to count how many turns each one has taken) and a directional gyro. This allowed both turn angles and distances travelled to ...
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  • 5,168
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 ...
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  • 12.1k
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 ...
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26 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 ...
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  • 46.6k
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 ...
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22 votes
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What is the deepest position in space we can get a GPS signal?

GPS is regularly used in low earth orbit. It is possible to use the signals from the sidelobes of the GPS transmit antennas to receive service in a high earth orbit up to and potentially beyond ...
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  • 9,929
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 ...
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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 ...
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18 votes

Can the satellites in Martian orbit be put to use providing a rudimentary GPS system on Mars?

Not the way GPS works, no, since the Mars orbiters don't have atomic clocks. (Though future Mars orbiters may someday.) The relay radios on the Mars orbiters provide a 2-way Doppler data type that ...
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  • 57.6k
18 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 ...
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  • 5,795
16 votes
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Accelerometer in space

Yes, a properly functioning accelerometer that is stationary relative to the surface of the Earth will read the acceleration due to gravity. If it's a very good accelerometer, you could also see the ...
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  • 57.6k
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, ...
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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 ...
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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 ...
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  • 64.7k
14 votes
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How does a rocket navigate during launch?

First of all, it's worth to mention that engine gimbaling is not the only way to control a rocket. You can use differential thrust, or vernier thrusters, or even aerodynamic flight control surfaces. ...
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  • 506
14 votes

How did astronauts navigate the Lunar Roving Vehicle (LRV) over the surface of the Moon?

Well if they did slip their navigation they can follow their tracks back to the LM. They planned for this in case of total breakdown, how much more for nav error.
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  • 834
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 ...
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  • 52.6k
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 ...
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12 votes
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Could a swarm of probes autonomously establish orbit around an asteroid?

Let's break your question into separate tasks: Autonomous orbit determination (autonomous because the DSN won't be there to help you when you need it) Autonomous attitude determination Situational ...
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  • 11.3k
12 votes

How could one navigate on Mars?

I'm a little surprised nobody has mentioned markers. As in flags, signposts, and splashes of paint on rocks. Astronauts on the first missions to Mars are not going to go all that far from their base. ...
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  • 20.8k
12 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 ...
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  • 118k
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 ...
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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 ...
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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 ...
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  • 1,941
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 ...
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  • 15.1k
11 votes

How does a rocket navigate during launch?

Rockets generally use an inertial navigation system (INS). This system uses the input from accelerometers and gyroscopes to calculate the rocket's position (relative to the launch pad) and attitude. ...
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  • 121k
11 votes
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How do probes locate themselves?

Interplanetary probes generally don't have enough equipment on board to calculate their own position. So the location of a probe is measured by ground control, using data from the probe. Distance ...
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