Questions tagged [guidance]

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

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29
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2answers
3k views

How did the Apollo guidance computers deal with radiation?

I was wondering how the Apollo guidance computer handled the radiation encountered in space
24
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2answers
16k 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 ...
24
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4answers
5k 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? ...
22
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3answers
4k views

Fortran and the Apollo 11 mission

I was just wondering, as a Fortran user. As far as I know, the simulations taken in order to carry the Apollo 11 mission was written in Fortran 2. I would like to confirm this from a reliable source. ...
22
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1answer
4k views

Who developed the mathematics used to correct the trajectory of Apollo 13?

The 1967 NASA technical note D-4246, Midcourse Guidance Procedure with Single Position Fix Obtained From Onboard Optical Measurements describes correcting the trajectory of a spacecraft traveling ...
22
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2answers
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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 ...
22
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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 ...
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 ...
17
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1answer
2k views

What were the differences between Space Shuttle's and Buran's reentry guidance?

Assuming unpowered flight, what were the significant differences between the STS orbiter and the Buran in: re-entry trajectory? re-entry guidance? navigation during re-entry (inputs and algorithms - ...
16
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1answer
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Soyuz Steering during Re-Entry

In this youtube video, it talks about steering Soyuz by changing lift. Why does roll rotation help in changing lift and also helping in cross range steering? I am looking for an answer from ...
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2answers
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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/...
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2answers
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Did the 1202 error and associated reboot prevent disaster on Apollo 11 landing?

Most accounts of the famous 1202 error reported by the AGS during landing of the Apollo 11 LM characterize the event as result of the successful operation of the AGS, flushing an resetting an ...
13
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1answer
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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 ...
12
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1answer
2k views

Double redundancy for the Saturn V LVDC computer memory, how were disagreements resolved?

In the Smarter Every Day video How did NASA Steer the Saturn V?- Smarter Every Day 223 Destin is talking with Luke Talley about the memory modules used in the Saturn V LVDC computer. This computer ...
12
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1answer
962 views

Could the Apollo Lunar Module be flown to a landing without the LEM Guidance Computer?

Inspired by answers to Could the lunar module have moved to a different spot? question but not talking about that specific relaunch scenario: Could the LEM stack (descent configuration) be flown ...
12
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1answer
795 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 ...
10
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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 ...
9
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1answer
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Rocket launch: closed vs. open loop?

I've seen many comments that pitchover and gravity turn are "open loop" and that powered explicit guidance (PEG) leading up to orbital insertion are "closed loop." And this has me ...
9
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1answer
880 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 ...
8
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2answers
925 views

Does terminal velocity play a significant role when launching from Earth?

As mentioned in the question Climbing at terminal velocity minimizes losses? But why? And "of what"? terminal velocity is important when launching space craft from Kerbal (Game Kerbal Space ...
8
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1answer
707 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, ...
8
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1answer
350 views

How does Schiaparelli's guidance system work?

I was not able to find any technical documentation on the closed loop guidance system that was supposed to accomplish the powered descent of ESA's Schiaparelli Entry Demonstrator Module. Several ...
8
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1answer
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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 ...
8
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1answer
630 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 ...
8
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1answer
387 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 ...
8
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1answer
423 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 ...
7
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1answer
728 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 ...
7
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1answer
531 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 ...
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 ...
6
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3answers
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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 ...
6
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3answers
2k views

How are IMU positions decided for rockets and spacecraft?

I imagine that engineers have to decide where an inertial measurement unit (or just an accelerometer, gyro, etc.) is placed in a rocket or spacecraft. I'd like to know how are these positions decided? ...
6
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1answer
325 views

Modeling attitude control: ramping/easing between attitude commands?

Say you switch from your current guidance program to a brand new program that commands your spacecraft to a different attitude. Assume the new attitude is a discontinuous step change from your ...
6
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1answer
325 views

Apollo guidance

I am studying the Apollo Guidance, specifically the derivation of guidance equation. While laying the baseline, a Target-referenced time (T) is chosen as time variable for guidance calculation of the ...
6
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1answer
340 views

Guidance vs. Navigation vs. Estimation

I'm still confused over what exactly falls under the scope of Navigation, Guidance, and Estimation systems. Say I have a bunch of IMUs and use them to determine my position and orientation and my ...
6
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2answers
281 views

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

The Apollo LM had a radar altimeter which was particularly critical in the final stages of landing. It could be set to two different pitch angles, either aimed backwards by 24º to be used during the ...
6
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1answer
298 views

Gravity turn: How to reorient along zero angle of attack

I was doing some back-of-the-envelopish calculations on gravity turns. Now the basics are clear to me (I think), but this detail escapes me: After liftoff we perform pitchover manouvre at time T+x, ...
6
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1answer
460 views

How did the upper stage of the Juno 1 rocket change its orientation while it was spinning?

The upper stage of the Juno 1 rocket was spun up to a high speed prior to launch so it would be spin stabilized and not require a guidance system. After the upper stage separated from the 1st stage it ...
5
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2answers
384 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 ...
5
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2answers
205 views

Interpolation method in pitchover maneuver: what type?

Consider the space shuttle or the Saturn V. Launch would begin with an open-loop pitch schedule obtained from simulation with the day’s winds. The pitch schedule would be specified as a lookup table ...
5
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1answer
296 views

What was back-up plan in case of Apollo CSM Primary Guidance System IMU went to gimbal lock?

In Apollo-11, during preparations for docking with Command and Service Module in lunar orbit, Armstrong and Aldrin managed to put Lunar Module Primary Guidance System Inertial Measurement Unit (IMU) ...
5
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1answer
244 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 ...
5
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4answers
578 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 ...
5
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1answer
1k views

Saturn V ascent guidance (simulation)

A while ago, I did a Saturn V ascent simulation in Matlab. The catering for drag, gravity and thrust vectors and mass depletion worked well, but I struggled to implement ascent guidance. I duplicated ...
5
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0answers
761 views

Why would someone use Modified Rodrigues Parameters over Quaternions for spacecraft attitude estimation? And vice versa?

I see quite some papers on spacecraft attitude determination and control, that rely on quaternions. While some others rely on MRPs. The advantage that I see so far is that... for quaternions, the ...
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0answers
157 views

Small-bodies landing strategies

Looking at past landing missions on small bodies such as Eros, Itokawa and 67P I found different landing strategies Eros: NEAR Shoemaker probe performed 4 impulsive pre-planned open-loop maneuvers to ...
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0answers
231 views

Lunar Descent and Landing Simulation

I am trying to simulate lunar descent and landing as a part of my undergraduate project. For time being, I have included gravity turn guidance scheme and used these equations Now, I can solve ...
4
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2answers
823 views

Generally, what types of sensors are used in rocket guidance systems?

I was wondering how a rocket adjusts its position to ensure it takes the desired path. What sensors, or generally technology, are used to gain data on the rocket's position, where it is heading and ...
4
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1answer
458 views

How does an Atlas V control roll?

My understanding is that you want to control roll in a rocket, along with the other directions. An Atlas V has a single RD-180 engine but I didn't see anything about vernier engines. I guess the RD-...
4
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1answer
1k views

Best practices for rocket ascent trajectory guidance

I thought I would ask what the most used methods in industry are, in order to guide a launch vehicle into a desired circular orbit at engine cutoff. It seems that the use of direction collocation ...
4
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0answers
63 views

Optimal Trajectory for SLV in the last stage

I have developed an algorithm for SLV guidance using optimal control theory. I need a reference trajectory to verify my algorithm. The algorithm requires the initial position and velocity coordinates ...