# Questions tagged [guidance]

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

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### How does a Space-Stabilized Inertial Navigation System actually torque its gimbals?

I've been trying to make a fairly-accurate video (with 3D animations coming soon) about Inertial Navigation Systems (INS), in which I plan to cover all the details from each gyroscopes and ...
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### Calculating downrange and crossrange distance and velocity relative to a surface point

I've started to go about implementing a descent guidance algorithm I found in a 1997 paper by D'Souza. However, I've hit a snag. The coordinate system is in terms of downrange position ($x$, relative ...
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### What online courses teach you hands on AOCS GNC?

I am looking for online courses that teach you "attitude and orbit determination and control systems" and "guidance navigation and control" with a focus on satellites or space ...
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### How does JUICE navigate autonomously

Introduction To kick things off, I'd like to introduce myself as a 23-year-old novice learner when it comes to space exploration but I've been listening to astronomy-specific podcasts since 2022 and I'...
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### What caused the falcon booster landing failure during the CRS-16 mission?

On December 5, 2018 the Falcon 9 booster started spinning during the landing burn, and promptly appears to have soft landed on the ocean. While SpaceX stated that the booster could be reused it never ...
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### Powered Explicit Guidance - Why wouldn't it be used?

I keep reading that the Powered Explicit Guidance equations (PEG) (detailed in the Technical note linked below) is (an approximation of) the most efficient way to get to space. That being said, I know ...
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### Hohmann Transfer - Adaptive Guidance Law

Is there an equivalent adaptive guidance law for the Hohmann transfer as there is with the initial ascent profile for a rocket launch (e.g. Powered Explicit Guidance)? This is for a personal project - ...
1 vote
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### Guidance and control inputs in autonomous satellites

I would like to know which are the standard navigation data available on a small satellite (in LEO). In particular, I'm trying to understand which inputs I should consider for the Guidance&Control ...
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### How did "ACA Out of detent" work?

This is a related question about the words said during Apollo 11 as soon as the LM touched the ground. My question is specific to ACA out of detent As soon as the LM touched down on the surface it ...
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1 vote
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### Space shuttle digital signal processor (DSP): floating point or fixed point?

Digital signal processors can represent irrational numbers using fixed-point or floating-point data types. Fixed point means fixed number of decimal places, and floating point means floating number of ...
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### 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 ...
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### How did the Apollo guidance computers deal with radiation?

I was wondering how the Apollo guidance computer handled the radiation encountered in space
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### 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 ...
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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 ...
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### Could the flyaway of the Curiosity/Perseverance skycrane be aimed in a particular direction?

The Perseverance rover is collecting samples of Martian rocks and soil, which will be picked up and returned to Earth on a future mission. In this comment to another question, I note that the sample ...
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### Does SPICE function gftfov account for occultations?

I need to determine when an antenna on a spacecraft can see a ground station on Earth at particular epochs. I have generated all the necessary SPICE kernels necessary as well as using the NASA ...
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### Trying to modify a JPL guidance algorithm for the Mars Sky Crane and Mars 2020

I've been trying to implement a modification to the JPL guidance law that was used (or very similar to what was used) for the powered descent portion of the MSL mission and I'm struggling to figure ...
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### 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 ...
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### 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 ...
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### 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 ...
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1 vote
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### RCS or Reaction Wheel for a 30kg cubesat

I am working on the design of a cubesat, it weighs approximately 30 kg and I am doing the Navigation and Guide Control system. I was wondering if I had some blueprint for some RCS or Reaction Wheels ...
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### 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-...
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### 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 ...
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### 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 ...
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I'm 1st grade physics student. I have learnt about units, vectors, kinetics, kinematics, Newton's laws of motion, galileo frames of references: galilean transformation, conservation of energy, ...
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### 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 ...
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### 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, ...
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### Can reaction wheels be used for detumbling?

During orbit insertion, the satellite can start with a high tip-off rate which requires detumbling. From what I have read, detumbling is usually done using magnetorquers. I was wondering if ...
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### 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) ...
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### 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 ...
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### Iterative Guidance Mode (Saturn V ascent guidance)

I tried to implement the iterative guidance mode algorithm given in the paper "Development of the iterative guidance mode with its application to various vehicles and missions" by D. C. CHANDLER and I....
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### 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 ...
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### 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 ...
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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 AGC during landing of the Apollo 11 LM characterize the event as result of the successful operation of the AGC, flushing an resetting an ...
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### 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 ...
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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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### Satellite mission design/performance requirements to attitude/orbit control design specifications

Are there any good sources that discuss: the steps involved in deriving attitude/orbit control design specifications, from satellite mission design/performance requirements?
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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 ...
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### Stability of rocket during flight; why does the lift force change direction when the center of pressure moves?

I am currently learning about fins and the role they play in the stability of a rocket during flight. I came across a relatively minor problem. Here is one of the resources I'm looking at: http://www....
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### 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 ...
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### 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, ...
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### Lunar ascent module: Guidance Law [duplicate]

I was wondering if there was an optimal law for the thrust (magnitude and direction) during the lunar ascent. I have read many things about this topic in this forum but I still have some doubts. It ...
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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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### 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 ...
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### Apollo guidance computer ROM addressing using the ROM bank register, what is the bank register size?

The Apollo guidance computer had 36 K words of core rope ROM. To address 36864 words, a 15 bit memory address for up to 32768 words is not enough, 16 bits are needed. This Wikipedia article describes ...
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### How are Launch Ascent Trajectories and Reentry Constraints Being Implemented these days?

Historically, endoatmospheric guidance for launch ascent has been open loop and suboptimal. Recently, however, it seems as though there has been renewed interest in determining optimal endoatmospheric ...
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### 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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### How accurate can a satellite's orbit be?

How precise can an artificial satellite be when it comes to following the exact orbit in relation to Earth or hitting the same point above Earth in orbit? Which orbit would be the most stable for this?...
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### What are common guidance strategies for a finite orbital maneuver?

Suppose we have our spacecraft in a circular orbit around the Moon and we want to transfer it to an elliptic orbit with a medium-thrust (10-100N) retrograde burn. Based on the current state estimate, ...
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