# Tag Info

## Hot answers tagged guidance

49

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. Let's start with the memory: Changing a bit in current S(D)RAM cells is trivial - introduce a bit of charge in the wrong place and the bit is lost. This ...

42

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 have changed as well. Let's start with a nice shot of the Mod 3 design on a Falcon 1.1 Full Thrust. You can see the size, shape, and design differences in ...

35

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 the 2016 movie Hidden Figures, honouring the women that were instrumental in the early days of the US space program. Katherine Johnson and her colleagues were ...

29

I worked at the MIT Instrumentation Lab during the Apollo program. Although I did not work on that program, I knew many of the people who did. The guidance computers for the command module and lunar landing module were each programmed in their own assembly language. The missions were exhaustively simulated on a large IBM 360 Model 75 computer, using a ...

29

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, including the Apollo Command Module, have used this offset-mass approach to generate lift, thus achieving some measure of control over the atmospheric flight ...

20

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 whose address is $10_8$ or greater contains an even number of "ones." All locations of $10_8$ or greater are stored in fixed or erasable memory with odd parity. ...

18

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 while the solid rocket engines are attached. After solid separation, roll control is performed by a set of 400 newton hydrazine thrusters located on the Vehicle ...

17

"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 (AGS). I'll be using the LM Apollo Operations Handbook Volume I as the main source for all your specific points. An attitude / attitude rate reference is ...

15

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.

14

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 Mahmud Pathan, Chalmers University of Technology (PDF). I'm reproducing here an excerpt that's most relevant to your question, and I'd recommend reading the ...

14

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 memory to the registers. That is, the data in the memory was assumed to be correct, and the error was assumed to take place between the electronics that ...

13

The Apollo 8 onboard clock's measured drift was $0.953\ ms/hr\ (0.26\ ppm)$, while the specified limit is $7.2\ ms/hr\ (2\ ppm)$. They also mention that there were "periodic clock updates from the ground" indicating that they accounted for the drift and over the mission time of 143 hours. Text transcription:     Computer.- Computer ...

13

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 @Uwe's answer. However, the programmers at the Real-Time Computing Center back in Houston then adopted the algorithm to process tracking data of the LM, naming it ...

12

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 constant during ascent. To proof this I will first have to define the required thrust, $F$, which has to overcome gravity and drag (such that the sum of all ...

11

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 holding to the accuracy of below a meter. It has four engines all of which can rotate 360 degrees and operating continuously to hold the position, to hold both ...

11

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 are actually doing it). Almost certainly the initial location is sent by Mission Control, refined the whole time. The ASDS is set to maintain a location, the ...

11

In my youth, I am now retired, I worked on the apollo program at north american space and information systems in downey calif. chief contractor for the Apollo Command/Service Modules. I also worked at Rocketdyne that was a part of north american. All the code I used and developed at that time was in fortran. The fortran programs performed analysis of test ...

11

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 second stage flight." Reference: DESCRIPTION AND PERFORMANCE OF THE SATURN LAUNCH VEHICLE'S NAVIGATION, GUIDANCE , AND CONTROL SYSTEM (first page of ...

11

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. (The ephemerides data was loaded on the computer's erasable memory pre-launch). There is a couple of subroutines called LSPOS and SOLPOS in ...

11

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. This wouldn't work, because there are a number of factors that cause trajectory deviation that can't be predicted. For example, engines can slightly over- or ...

10

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 acceleration trigger, which is chosen to keep the deployment within the required Mach-dynamic pressure box over the dispersed entry conditions. The parachute ...

10

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-sensitive. Spacecraft Guidance, Navigation, and Control Requirements for an Intelligent Plug-n-Play Avionics (PAPA) Architecture : In the first stage after ...

10

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 way to orbit. If your only objective were to gain altitude, then you would go straight up and, while drag matters, try to track your terminal velocity at the ...

10

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 have enough information to know if the situation could have existed on Apollo 11. I think we know it did not exist on Apollo 11, because the radar power supply ...

9

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 is that the system can no longer distinguish the axes of rotation properly, so can't tell how the orientation is changing. The remedy for gimbal lock is just ...

9

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. The solution is simple: Don't do that. There's typically no reason to make (for example) a 180° rotation in the minimum amount of time required. Many vehicles ...

9

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 crash or the crew becoming stranded in space. Once the spacecraft left Earth's atmosphere, the risks increased exponentially due to large amounts of radiation ...

8

ONBOARD COMPUTERS: The Buran's computer is cadenced à 4MHz (3 MHz for STS), consisting of 4 independent units and 5 independent units on the shuttles. the dead memory is stored on magnetic tapes, the memory of the Buran's computer is 819 200 words of 32 bits and for shuttle 106 496 words of 16 bits which give buran a better calculation power. Shuttles ...

8

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 oscillations at the end of the run. The early switchover to the next phase just avoids this effect. "The part actually flown" means the part flown under that segment ...

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