Questions tagged [guidance]

Questions which relate to how spacecraft and rockets navigate and stay on course.

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24
votes
4answers
4k views

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

The descending Falcon 9 has got to hit (preferably gently) the tiny target of the Autonomous Spaceport Drone Ship (ASDS) in the middle of the ocean. How does the Falcon 9 know where the ASDS is? ...
24
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2answers
15k views

How are the SpaceX Falcon 9 Mod 3 and Mod 4 grid fins different?

Elon Musk tweeted "Flying with larger & significantly upgraded hypersonic grid fins. Single piece cast & cut titanium. Can take reentry heat with no shielding." These have been commonly known ...
6
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3answers
2k views

Is aerodynamic lift ever useful in rocket flight?

When a rocket is traveling through an atmosphere, the component of the aerodynamic force in the direction of motion is called drag, and the component perpendicular to that is called lift. Usually a ...
7
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1answer
2k views

Coefficients for linear tangent steering law

Given certain simplifying assumptions, a "linear tangent" steering law is optimal for orbital insertion of a launch vehicle: $$\tan \psi = a\cdot t + b$$ i.e. the tangent of the flight path angle ...
8
votes
1answer
522 views

How does the Apollo LM ascent guidance program P12 actually work?

P12 is the AGC guidance program for normal ascent from the lunar surface to orbit. According to the mission planning documents, after separation and ignition, the ascent stage holds its initial ...
5
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4answers
480 views

How can a deep-space spacecraft determine in real time the direction of delta-v?

My spacecraft knows it wants to add a certain delta-v in a certain direction to its motion, relative to the stars. It will calculate current mass based on propellant usage history, which hasn't been ...
22
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2answers
4k views

How did the Apollo guidance computer handle parity bit errors?

The following answers mention the use of parity bits in the Apollo guidance computer: this answer to Bits per core for the different versions of the Apollo guidance computer core rope memory? this ...
7
votes
1answer
617 views

How did the Apollo guidance computer handle the Earth-Moon system's rotation around the Sun?

In this comment I just wrote: "...but at all other times it is just doing math to calculate its trajectory." The math needed a stable clock Timing accuracy of the Apollo Guidance Computer? (also 2, ...
10
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1answer
646 views

Timing accuracy of the Apollo Guidance Computer?

The AGC timing reference came from a 2.048 MHz crystal clock. But how accurate was this clock circuit? Note 3 of this schematic: "The value of the follwing components to be determined at unit test" is ...
8
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1answer
359 views

Apollo-11 delta-v “due to residual pressure in the docking tunnel pushing the spacecraft apart” detected as it happened? Was it corrected?

This answer to How far off did Apollo 11 land? mentions that: Eagle was already 3 miles downrange from the expected position at the start of descent, due to residual pressure in the docking ...
2
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2answers
608 views

Rocket drag and lift based on flight direction - in which frame of reference?

Drag is aerodynamic force component parallel to the direction of motion. Lift is aerodynamic force component perpendicular to the direction of motion. Direction of motion with respect to what? 1) ...
21
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2answers
8k views

How did NASA remotely fix the code on the Mars Pathfinder?

In 1997, NASA remotely fixed a bug that caused priority inversion on their Mars Pathfinder. How did they go about doing this? What kind of communication protocols are used? How do they update the ...
11
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1answer
2k views

Climbing at terminal velocity minimizes losses? But why? And “of what”?

A lucky discovery of a Kerbal engineer's writing gave this deep insight into the mechanics of climbing to orbit: the best way to minimize d/v losses through the atmosphere is to always go at ...
8
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1answer
351 views

Bits per core for the different versions of the Apollo guidance computer core rope memory?

The first version of the Apollo guidance computer had a ROM of only 12 K words of 16 bit. Later it was doubled to 24 K and finaly tripled to 36 K words. The first version of core rope read only ...
8
votes
1answer
829 views

What is the maximum acceptable latency in rocket control computers?

Rockets require real-time computers, in that there are operational deadlines between events and system response. How quickly does the rocket's controller need to respond to sensors and events, without ...
15
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2answers
2k views

What is a “Lear Processor” and how did it work?

This answer to the question What was the mascon “fix” used by Apollo 12? says (in part): The Tindallgrams have some notes on the matter. See pages 307 to 354 of http://www.collectspace.com/resources/...
8
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1answer
1k views

Machine Learning and Classical Navigation, Guidance and Control in Space Exploration

Due to the increasing availability of large quantities of data and computational power, machine learning (ML) is providing increasingly better results in various fields. Much research has been done on ...
20
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1answer
3k views

How do single engine rockets control roll?

While it's obvious how a single gimbaling engine can control a rockets attitude, it is less clear how it could control roll. Nonetheless many rockets use just a single main engine with no fins or ...
7
votes
1answer
459 views

How does rocket guidance deal with changing mass?

The first stage of the Saturn V, for example, burned about 26 tons of material in total per second (https://en.wikipedia.org/wiki/Rocketdyne_F-1#Specifications). Therefore the rocket dynamics are ...
5
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2answers
315 views

Launch profile autopilot

I'm new here, and I am delighted this forum exists! I'm working on a spaceflight simulator (FSX SpacePort) and currently, developing automated guidance module (I guess, a space autopilot). The ...
3
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1answer
543 views

Samples of old guidance software using computational resources on Earth implementing navigation in space

Answers to Given small computational resources how navigation was implemented ( Not Samples of old guidance software) are excellent. I was stunned to see an article mentioning 65KB was used to ...
9
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1answer
2k views

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

The Space Shuttle had several aerodynamic control surfaces to control it during reentry and the final phase of atmospheric flight to landing. It seems a waste to haul tons of control surface to orbit ...
6
votes
1answer
206 views

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

This answer to a related question suggests that the order in which rotations around three principal axes are applied (in order to estimate the conversion of an attitude to a set of roll, pitch and yaw ...
6
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1answer
650 views

Saturn launch precautions for clearing tower?

In watching some Saturn rocket launches from the perspective of the camera being on the launch tower, it seems as if there was relatively little distance between the launching rocket and the tower. I ...
3
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2answers
190 views

Confusion with Apollo CSM attitude maneuvers (roll, pitch and yaw) during coasting to/from the Moon

Some time after Transposition, Docking, and Extraction maneuver (when coasting to the Moon) or after Trans Earth Injection (when coasting back from the Moon), the spacecraft's (CSM) guidance platform ...