# Tag Info

### 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....
• 13.3k
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 ...
• 76.7k
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 ...
• 12.4k
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, ...
• 18k

### 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 ...
• 46.6k
Accepted

### How do single engine rockets control roll?

The Ariane 5 launches with two strap-on solid rocket boosters. The thrust vector control on these solid rocket boosters provides the necessarily roll authority during the first 130 seconds of flight ...
• 65.6k
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 (...
• 1,941
Accepted

### Were the aerodynamic control surfaces of the Space Shuttle used during ascent?

They were used, but not to alter the flight path - rather, to reduce aerodynamic loads on the vehicle structure, particularly hinge moment loads on the elevons. This is known as load relief.
• 9,949
Accepted

### 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 ...
• 75.6k
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 "...
• 5,078

### 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 ...
• 5,847
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 @...
• 46.6k
Accepted

### Climbing at terminal velocity minimizes losses? But why? And "of what"?

Climbing at terminal velocity is the most fuel efficient speed to gain (vertical) height while in steady state, such that the density, velocity, gravitational acceleration and other parameters stay ...
• 707

### 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

### 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 ...
• 76.7k
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 ...
• 160k
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....
• 2,682
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 ...
• 160k

• 161k
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 ...
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 ...
• 57.7k
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-...
• 161k
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 ...
• 161k

### 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. ...
• 65.6k

### 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 ...
• 930
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 ...
• 161k
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 ...
• 161k
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 ...
• 335