Skip to main content
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....
asdfex's user avatar
  • 15.1k
42 votes
Accepted

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 ...
geoffc's user avatar
  • 79.9k
34 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 ...
Ludo's user avatar
  • 14.4k
30 votes
Accepted

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, ...
Tom Spilker's user avatar
  • 18.3k
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 ...
DrSheldon's user avatar
  • 48k
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 (...
indy91's user avatar
  • 1,991
14 votes
Accepted

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 "...
Mark Omo's user avatar
  • 5,291
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 ...
Michael Stachowsky's user avatar
13 votes
Accepted

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 @...
DrSheldon's user avatar
  • 48k
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 ...
hshib's user avatar
  • 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 ...
Organic Marble's user avatar
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....
Diego Sánchez's user avatar
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 ...
Organic Marble's user avatar
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. ...
Russell Borogove'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
Accepted

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 ...
Russell Borogove'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
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 ...
und3niable's user avatar
9 votes
Accepted

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 ...
MICRO-DownUnder's user avatar
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 ...
Russell Borogove's user avatar
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 ...
Russell Borogove's user avatar
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 ...
Russell Borogove's user avatar
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 ...
DrSheldon's user avatar
  • 48k
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 ...
Przemek D's user avatar
  • 375
7 votes

How does the Falcon 9 know where the landing barge/pad is?

The stage and ship both navigate to a preprogrammed GPS coordinate. It seems that GPS datum cannot be changed in-flight. Last-minute corrections are done via a radar on the stage. AOS by the drone ...
Hobbes's user avatar
  • 128k
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 ...
Mark Adler's user avatar
  • 58.2k
7 votes

What is a "Lear Processor" and how did it work?

According to this page William Lear, an aerospace engineer wrote a Kalman filter program for Apollo 11 Lunar Module computer. In particular, the on-board computer that guided the descent of the ...
Uwe's user avatar
  • 49.2k
7 votes
Accepted

How exactly was Apollo CSM attitude changed (from a current one to a new required one)?

A single axis rotation (SAR) was performed from the initial to final attitude, unless they were avoiding gimbal lock, in which case it was split into two rotations. It has been shown in MIT/IL ...
Organic Marble's user avatar
7 votes
Accepted

Did the Apollo LM's cockpit altitude displays account for the pointing angle of the radar altimeter?

Yes and No. The altitude data presented on the altitude indicator (tapemeter) depends on the mode select switch setting. MODEL SEL switch LGD RADAR: Radar altitude, altitude rate... are displayed. ...
indy91's user avatar
  • 1,991

Only top scored, non community-wiki answers of a minimum length are eligible