Skip to main content
49 votes
Accepted

How did the X-15 control attitude above the Kármán line?

The X-15 had a reaction control system for all three axes using thrusters with hydrogen-peroxide monopropellant. There was an automatic as well as a manual mode. The manual mode used a single three-...
Uwe's user avatar
  • 49.2k
40 votes

How did the X-15 control attitude above the Kármán line?

The X-15 has a reaction control system. In this image, it's item 2, 13 and 28, labeled 'ballistic control system'. It was operated via a joystick. Detail of two of the thrusters:
Hobbes's user avatar
  • 128k
37 votes

What is the "pendulum rocket fallacy" as it relates to analogizing a pencil balanced on a finger to maintaining attitude of a hovering rocket?

The pendulum fallacy is the belief that rockets would be passively stable with engines at the top, with the rocket "hanging" from them. The error lies in expecting gravity to pull the body ...
Christopher James Huff's user avatar
37 votes

Why do Canopus Star Trackers track Canopus? Why not so Sirius?

As someone who has designed a Canopus tracker, it's really very simple. The Sun is generally the easiest thing for a spacecraft to orient to, regardless of orbit or location in the Solar System. So, ...
John Doty's user avatar
  • 3,604
33 votes

Why do Canopus Star Trackers track Canopus? Why not so Sirius?

This answer assumes that the spacecraft is in an orbit which is mostly aligned to the ecliptic plane. A target, whose orbit is also close to the ecliptic plane, can occasionally go in front of the Sun ...
AJN's user avatar
  • 1,030
25 votes
Accepted

How do Voyager 1's Trajectory Control Thrusters differ from its Attitude Control Thrusters?

The attitude thrusters and TCMs are mechanically identical, all Aerojet MR-103s. From the Voyager Press Kit: The 16 thrusters on the mission module each deliver 0.89 N (0.2-lb.) thrust. Four are used ...
Russell Borogove's user avatar
25 votes
Accepted

Why does the Psyche Spacecraft use cold gas thrusters?

It's like looking for a needle as all eyes are on the Hall thrusters. TL;DR: Why does the Psyche Spacecraft use cold gas thrusters? Psyche was always designed for the main propulsion to be electric ...
blobbymcblobby's user avatar
24 votes

What is the "pendulum rocket fallacy" as it relates to analogizing a pencil balanced on a finger to maintaining attitude of a hovering rocket?

In the inverted pendulum problem: gravity exerts a vertical force on the pendulum, at the center of gravity the support of the pendulum (like the finger under the pencil) exerts a vertical force on ...
njzk2's user avatar
  • 368
18 votes

What does "reaction" in "reaction control system" and "reaction wheel" refer to?

I think there is little doubt that "reaction" refers to the "equal and opposite reaction" of Newton's third law. First consider "reaction control system". In principle, ...
Mark Foskey's user avatar
  • 11.4k
14 votes

Why two engines on stage 2 of New Glenn if it's disposable?

In 2015-2016, the New Glenn design was expected to use a single BE-4 methane-LOX engine on the second stage (about 2400kN thrust), and a single BE-3 (the same as the suborbital New Shepard's single ...
Russell Borogove's user avatar
13 votes
Accepted

Did NASA tell the Skylab astronauts to "Stop running around!"?

I think they did (page 120): The reference is a bit indirect, but the water storage was right next to the 'exercise ring' (storage lockers):
Hobbes's user avatar
  • 128k
12 votes
Accepted

Does this kill vehicle contain momentum wheels? Watch how it moves!

The thruster configuration can be seen better in this image:(cropped from this document ). The attitude control thrusters are not in plane with the direction control thrusters. This Raytheon patent ...
Andreas's user avatar
  • 1,395
12 votes
Accepted

How did the Canopus Star Tracker work? Are there any still out there in service today?

As you rightly point out in your question, Canopus star trackers are pretty nifty instruments. I don't think it's really possible to do them justice in a single post, so I'll include a few summarizing ...
RaptorChief's user avatar
  • 1,275
12 votes
Accepted

Does the Merlin vacuum engine on SpaceX's Falcon 9 gimbal?

According to the Falcon Payload User's Guide posted on the SpaceX website, the 2nd stage engine gimbals. (Emphasis mine)
Organic Marble's user avatar
11 votes
Accepted

Could the ISS stop rotating wrt the stars for a few days, then start again?

This is not a full answer, but some numbers: What are the ISS moments of inertia around design axes? The total moment of inertia of the station is about $M = 55\cdot 10^6 \rm kg m^2$ How often must ...
asdfex's user avatar
  • 15.1k
11 votes
Accepted

Does the "Tennis Racket Theorem" apply to the ISS? Does it rotate around its intermediate (unstable) axis?

Does it have three unequal principal moments of inertia... Does the ISS have three distinct principal moments of inertia? The answer is definitely "yes". Any object has a mass matrix, $M$. In three ...
Ludo's user avatar
  • 14.4k
10 votes
Accepted

Has a spacecraft ever used a four gimbal gyroscope? Did Michael Collins get his Christmas wish?

The Shuttle Orbiter's Inertial Measurement Units (IMUs) had four gimbals. The IMU consists of a platform isolated from vehicle rotations by four gimbals. Since the platform does not rotate with ...
Organic Marble's user avatar
10 votes

Has a spacecraft ever used a four gimbal gyroscope? Did Michael Collins get his Christmas wish?

Gemini had a four-gimbal system as well: The IMU is the usual gimballed stable platform with accelerometers and angular resolvers as in Apollo, except for a key difference that the Gemini IMU had ...
Russell Borogove's user avatar
10 votes
Accepted

How "hard" did Apollo 12 turn left just before it landed?

Without any time markings, it's impossible to tell if the ground track indicates a "hard left" or very gentle maneuvers over a long period of time. The annotated transcript gives us some ...
Russell Borogove's user avatar
10 votes

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. ...
David Hammen's user avatar
  • 75.2k
9 votes
Accepted

How hard was it for the Shuttle to perform attitude control for the entire ISS? Did they have to calibrate?

I'm interpreting this question as "Did adjustments have to be made to the shuttle Digital Autopilot (DAP) while it was controlling the mated stack (shuttle + ISS) - i.e. was a maneuver tried, the ...
Organic Marble's user avatar
8 votes

Could the ISS stop rotating wrt the stars for a few days, then start again?

I don't think it's happened in a long time, but in the early stages of assembly, the ISS sometimes flew in a "XPH" attitude when the beta angle* was between 10 and 75 degrees. The only public info I ...
Organic Marble's user avatar
8 votes

Could this three-thruster spherical spacecraft de-tumble itself with zero final velocity?

No, this wouldn't work. If the craft is initially at rest, then after firing the middle thruster, it could never stop spinning. Let's say the three thrusters have torque vectors +x,-x,+y, in a ...
mr_e_man's user avatar
  • 281
7 votes
Accepted

Why did Cassini have reaction wheels but Galileo, Juno and New Horizons don't?

It boils down to: how much spacecraft resource is required by the attitude control method you propose using? And sometimes the mission's pointing requirements play a significant role. Thrusters use ...
Tom Spilker's user avatar
  • 18.3k
7 votes
Accepted

How will NEA Scout control its attitude during deep space flight & keep its camera steady without vibrations or damage to its 85 m² solar sail?

The NEA Scout contains multiple items aimed at controlling attitude: An inertial measurement unit that contains rate gyros that sense the vehicle's rotation rate with respect to inertial, A star ...
David Hammen's user avatar
  • 75.2k
7 votes
Accepted

What do/will "quantum gyroscopes using nitro­gen-vacancy centers in diamond" for space applications actually look like, and how do they work?

(Disclaimer: I'm just a software engineer that happens to work in a quantum research center. This answer is based on my understanding of NV centers, which is limited to what I need to know for my ...
Ludo's user avatar
  • 14.4k
7 votes

Understanding and breaking down pointing requirements

In my professional experience in writing spaceflight software requirements, reading them, implementing them, validating them, and verifying them, these "what does that mean" questions come ...
Erin Anne's user avatar
  • 12.2k
6 votes
Accepted

Why are the ISS attitude values shown on these two web sites so different?

The conversion of the attitude data as it appeared (undocumented) from Lightstreamer to roll, pitch, and yaw was the biggest pile of guesses and assumptions atop assumptions I made back when Matt and ...
Yuri Gadow's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible