41 votes
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How can a sounding rocket accurately take the temperature of the atmosphere while flying through it at high speed?

According to the link here, In meteorological rockets, the temperature sensor is not measured as the rocket ascends but a payload containing the sensor is ejected from a high altitude and as it ...
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25 votes
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Why did NASA collect so much data about electrical phenomena at the Apollo 13 launch site?

According to an article from the Lunar and Planetary Institute (archive.org link): As a result of the electrical disturbances experienced during the Apollo 12 launch, several experiments were ...
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23 votes
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If I wanted to reconstruct an entire Apollo mission's crewed spacecraft trajectories, what are the key sources of historical data I'd look for?

To answer the question literally: you'd be looking for NASA Apollo Trajectory (NAT) data files. The report Apollo Mission 11, Trajectory Reconstruction and Postflight Analysis Volume 1 (PDF) provides ...
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19 votes
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How do we know what percentage of NEOs we've discovered?

NEOs are mostly found as dots in images taken by various telescopes, often those of amateurs (as in not paid, nothing about skill or equipment). By taken repeated images days apart moving dots can be ...
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16 votes
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Accelerometer in space

Yes, a properly functioning accelerometer that is stationary relative to the surface of the Earth will read the acceleration due to gravity. If it's a very good accelerometer, you could also see the ...
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  • 57.5k
12 votes

How can a sounding rocket accurately take the temperature of the atmosphere while flying through it at high speed?

Here is an answer from over on aviation.stackexchange.com which addresses this issue. I've quoted a portion of it below, but see that link for more info. As you measure temperature moving at high ...
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  • 1,138
11 votes
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Fuel vs food on the trip to Mars?

Fuel requirements will probably dominate food and other consumables by an order of magnitude or more, so you can't save mass by shortening the trip. The exact tradeoff depends on the assumptions you ...
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10 votes
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Rocket Propulsion Elements: Total Impulse Problem

You got caught by those silly English units. Your expression, $I_t = I_{sp}g_0 \dot m \Delta t$, works just fine when you use metric units. The mass flow rate, in metric units, is 127 kg/s. The total ...
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  • 62.9k
9 votes
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How is foot-pounds of energy defined?

Is it... the gravitational potential energy of one pound hoisted one foot in a constant gravitational field...? Yes indeed it is! To be energy, the pound has to be parallel to the foot. $$E = \int \...
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  • 148k
8 votes

Has an interplanetary date/time system been established yet?

In contexts in which there are virtually little relativistic effects, the current standard Coordinated Universal Time (UTC) would apply. As long as communication could be established with Earth, times ...
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  • 23.5k
8 votes
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What are these structures on the Lunar Ranging Retro Reflector (LRRR) arrays for?

The Apollo 11 EASEP handbook gives basic information on the first version. Of the LRRR, it has just two pages of text... There are some (poorly reproduced) images labelling the main parts. It's ...
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  • 5,148
8 votes
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How precise are spacecraft trajectory measurements?

The injection accuracy of the launch vehicle is typically measured in m/s, as the velocity change required to get the spacecraft exactly on the desired trajectory. This wraps up all the dimensions of ...
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8 votes
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What is the order of magnitude forces due to Earth's magnetic field, sunlight, drag, oblateness and tidal forces compare?

Here is a nice graph of part of what you are asking for. It's from the book Satellite Orbits; Models, Methods, Applications by Oliver Montenbruck and Eberhard Gill, Springer, 2000. The figure and ...
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7 votes
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How are precision trajectory measurements made of trans-Neptunian spacecraft?

Doppler and ranging are used routinely. They are both two-way, with the Doppler turning the frequency around and the ranging turning around a pseudo-noise signal. This is complicated, only for these ...
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7 votes

What forms of water ice have been observed and verified in the solar system?

Actually, Ice VII has been discovered in diamonds on Earth. The water is first trapped in the diamond as the latter is formed deep in the mantle. Then when the diamond cools at the surface its rigid ...
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  • 6,882
7 votes
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What forms of water ice have been observed and verified in the solar system?

The only form of ice that we see naturally in bulk on Earth is Ice I, all within the sub-h variety. There's no place on Earth that gets cold enough for any other form--but that's not necessarily true ...
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7 votes
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How can an orbiting spacecraft's motions yield the orbitee's deep structure?

Gravimetric Doppler measurements can actually confirm that Vesta has an iron core, as it eliminates the alternatives. This works in the following way: The mass of Vesta is first measured accurately, ...
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6 votes

Sensitivity of Space Telescopes and Instruments

LISA (long PDF) uses interferometry. This is a method that allows very accurate measurement of the difference between two lengths. Basically, a laser beam is split. Each half of the beam travels a ...
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6 votes
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Has an interplanetary date/time system been established yet?

For the vast billions of people living in a relatively natural environment, our already insanely convoluted time systems in use on Earth are reasonably appropriate. For the foreseeable future, all ...
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6 votes
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How is real position of probes orbiting other planets measured?

Here is a good tutorial on the navigation of deep space vehicles. The two main data types used are two-way Doppler (using an atomic clock reference at the DSN station, with the frequency locked to ...
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6 votes

How does an atmospheric probe measure temperature during descent?

As described in extensive detail by Al Seiff and T.C.D. Knight in their May 1992 paper in Space Science Reviews, Vol 60; The Galileo Probe Atmosphere Structure instrument (which can be read without ...
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6 votes

How are IMU positions decided for rockets and spacecraft?

For spacecraft it's "where they fit and can be oriented properly". Harnessing constraints are somewhat considered (how do you get wires to it) and thermal constraints might be pretty important (ir ...
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  • 600
6 votes
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How will OSIRIS-REx scan and characterise the near-earth asteroid Bennu?

OSIRIS-REx is packed all full of good stuff. I'll throw together a quick list of the scanning ones you're interested in. Also of note is that the entire spacecraft will be making that scanning ...
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  • 1,246
6 votes
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How is atmospheric temperature measured from a satellite?

I'm not sure if I understand the basics behind this well enough to explain it but I'll give it a try anyway. I've looked mainly at this report and on the wiki on satellite temperature measurements. ...
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6 votes
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How would 2 spacecraft be launched to be in sync in opposite directions?

STEREO A and B, 2006-047A and B, (29510 and 29511) were launched together from "Cape Canaveral Air Force Station in Florida on a Delta II 7925-10L launcher into highly elliptical geocentric ...
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  • 148k
6 votes
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How can rockets measure their own speed relative to the ground?

You can put measuring devices anywhere you like, but the best answers are always computed by measuring many different ways simultaneously. If you have enough independent methods, you can detect and ...
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  • 5,197
5 votes

Could a Kuiper Belt object fly by probe measure star distances by parallax better than Gaia?

To use the longer base line of 100 AU instead of 2 AU, we need measurements from both the probe in the Kuiper Belt and another probe near the earth. But the data transfer over 100 AU distance is very ...
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  • 1,674
5 votes

How are IMU positions decided for rockets and spacecraft?

See NASA Technical Note D-5869. This document includes a discussion about choosing the location of the navigation instruments of the Saturn V rocket. See the figures on pages 11 and 13 and nearby text ...
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5 votes

How are IMU positions decided for rockets and spacecraft?

It depends upon the mission. Ideally you try to put them as close to the center of mass as you can so that you don't have that offset between the IMU and the center of mass to worry about, but these ...
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  • 831
5 votes
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Why do the LAGEOS' satellites have four germanium corner cube reflectors out of over 400?

D.A. Arnold "Optical and Infrared Transfer Function of the Lageos Retroreflector Array", 1978, NGR 09-015-002 (P179) confirms that they're for infrared measurements, and adds some interesting info: ...
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