50
votes
How did the Apollo guidance computers deal with radiation?
TL;DR: It was so busy getting stuff done, it didn't care.
Being old, slow, massive and inefficient (by any modern standards, not by those in 1965) is a huge benefit when it comes to radiation hardness....
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42
votes
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How are the SpaceX Falcon 9 Mod 3 and Mod 4 grid fins different?
Ok, I asked so I could use these awesome photos in an answer... I confess.
The material has changed from Aluminium with an ablative paint to bare titanium. The specific shape, size, and mount points ...
- 78.9k
35
votes
Accepted
Who developed the mathematics used to correct the trajectory of Apollo 13?
The authors of the paper are Harold A. Hamer, Katherine G. Johnson, and W. Thomas Blackshear. Of these, the name Katherine Johnson might ring a bell with people, as she was one of the protagonists in ...
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30
votes
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Soyuz Steering during Re-Entry
By itself the roll doesn't generate lift. But the Soyuz descent module (DM) enters with a non-axial center of mass that results in a non-zero angle of attack, and hence some lift. Several spacecraft, ...
- 18.1k
21
votes
How did the Apollo guidance computer handle parity bit errors?
1. How did the Apollo guidance computer handle parity bit errors?
According to Apollo 15 Hardware by Delco Electronics,
Parity Alarm
Occurs if any accessed word in fixed or erasable memory ...
- 47.4k
18
votes
Accepted
Could the Apollo Lunar Module be flown to a landing without the LEM Guidance Computer?
"Could be flown" is a clear yes, "could be flown to a landing" is another story. Most of the points you are listing can be accomplished using the backup system in the LM, the Abort Guidance System (...
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14
votes
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How did NASA remotely fix the code on the Mars Pathfinder?
Specifically, for the Mars Pathfinder priority inversion problem, this is explained in detail in Mars Pathfinder: Priority Inversion Problem, Report for the Seminar Series on Software Failures, Risat ...
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14
votes
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Timing accuracy of the Apollo Guidance Computer?
The Apollo 8 onboard clock's measured drift was $0.953\ \text{ms/hr}\ (0.26\ \text{ppm})$, while the specified limit is $7.2\ \text{ms/hr}\ (2\ \text{ppm})$. They also mention that there were "...
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14
votes
How did the Apollo guidance computer handle parity bit errors?
What a fascinatingly obscure question :-) It took some digging, so perhaps someone who's actually seen an AGC might know better:
The parity bit was used to verify that data transferred correctly from ...
- 6,200
13
votes
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What is a "Lear Processor" and how did it work?
It's an algorithm to speed up certain matrix operations, not a piece of hardware. It appears that the algorithm was first invented by William M. Lear for the LM guidance computer, as explained in @...
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12
votes
How does the Falcon 9 know where the landing barge/pad is?
The issue is interesting, since the Bezos patent is specific about the barge and the rocket handshaking and talking directly to each other. But SpaceX is contesting the patent (obviously, since they ...
- 78.9k
11
votes
How does the Falcon 9 know where the landing barge/pad is?
According to Musk at the post CRS-8 briefing:
Both (ship and rocket) is going to an absolute position. So the ship is holding to the absolute GPS position, with relative GPS and today it was ...
- 609
11
votes
Accepted
Saturn launch precautions for clearing tower?
Just as with Shuttle, the first stage guidance was pre-programmed to fly a specific flight profile. For Saturn V "guidance
corrections
are
not
introduced
before
the
early
part
of
the
...
- 174k
11
votes
Accepted
How did the Apollo guidance computer handle the Earth-Moon system's rotation around the Sun?
The Apollo Guidance Computer contained the position and speed of the Sun relative to the earth at launch time, and was able to calculate it's position at any given time after launch based on that data....
- 2,692
11
votes
Accepted
Did the 1202 error and associated reboot prevent disaster on Apollo 11 landing?
I agree with your comment "it's not clear when or if this situation actually occurred." From reading both Klumpp's account and his colleague Don Eyles' book Sunburst and Luminary I do not think we ...
- 174k
11
votes
Rocket launch: closed vs. open loop?
Your first guess was correct.
But it's also possible that instead of preloading the rocket's attitude profile, they would preload the engine nozzle actuator commands required to follow that path.
...
- 165k
10
votes
Accepted
Does terminal velocity play a significant role when launching from Earth?
No, launches don't specifically target terminal velocity. They target an optimized trajectory that minimizes the total propellant required to counter both atmospheric drag and gravity losses on the ...
- 58.3k
10
votes
Accepted
What is the maximum acceptable latency in rocket control computers?
The STS roll control program controlled attitude in response to sensed velocity, rather than attempting to control the trajectory directly. This portion of the flight wouldn't be particularly latency-...
- 165k
10
votes
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How does Schiaparelli's guidance system work?
The 2011 Thales Alenia Space presentation on EXOMARS-2016 GNC Approach for Entry Descent and Landing Demonstrator might have something that may help.
From that:
The parachute is deployed based on an ...
- 116
10
votes
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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 ...
- 375
10
votes
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Launch profile autopilot
Your general picture of ascent guidance is on track, but everything is complicated.
As soon as roll complete, pitch for gravity turn
The exact timing and initial pitch for the start of the gravity ...
- 165k
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. ...
- 71.8k
10
votes
How did the Apollo guidance computers deal with radiation?
The Apollo Guidance computer (AGC) controlled the jet propulsion and thus maintained the spacecraft's altitude and navigation. As you pointed out, any defects or errors in the AGC could result in a ...
- 940
9
votes
Accepted
What was back-up plan in case of Apollo CSM Primary Guidance System IMU went to gimbal lock?
The Apollo attitude control system starts from a known orientation established by taking star sightings, then uses gyroscopes to track the change in orientation over time. The problem with gimbal lock ...
- 165k
8
votes
Accepted
Apollo guidance
Because some of the terms in the guidance equations divide by time-to-go and/or the square of time-to-go, relatively small input (sensor) errors can yield large effects, causing large steering ...
- 165k
8
votes
Accepted
Is aerodynamic lift ever useful in rocket flight?
Angling to get lift is going to increase the atmospheric cross-section of the rocket and so increase drag. For any reasonable angle of attack, the drag force is going to be much larger than the lift ...
- 165k
7
votes
Coefficients for linear tangent steering law
The whole mathematical apparatus describing the rocket flight — gravity, rocket equation — it's a set of functions that take some parameters allowing you to model the process. If we set ...
- 375
7
votes
Is aerodynamic lift ever useful in rocket flight?
As far as I know, no. In order to make a cylindrical rocket as light as possible, they are flown to minimize the side loads to the structure -- as close to a zero angle of attack as possible. If they ...
- 58.3k
7
votes
How does the Apollo LM ascent guidance program P12 actually work?
Partial answer
To answer @Russell's subquestions:
My analysis isn't far enough yet to fully explain the attitude versus time calculations.
Although there are a lot of calculations done before the ...
- 47.4k
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