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9 votes
Accepted

Why do radar maps of the surface of Venus have missing slices?

These maps were produced with doppler-delay imaging, which uses a combination of range and motion to identify the radar return from each specific point on the surface and build a map. Longitude is ...
Quentin Clarkson's user avatar
7 votes

Has Same Beam Interference (SBI) been used or at least tested at Mars? Are there plans to use it in the next few years?

This seems to be reported by NASA - NTRS in a document on Orbiter-Orbiter And Orbiter-Lander Tracking Using Same-Beam Interferometry [Published 1992 Acquired 2013]: Two spacecraft orbiting Mars will ...
DialFrost's user avatar
  • 1,673
6 votes
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How does Deep Space Network's DSS-14 transmit radar and receive it at (almost) the same time? (monostatic radar)

Evidently the DSS-14 does rely on separate periods of transmitting and receiving, but it is able to switch between the transmitting and receiving modes rapidly using a "quasi-optical switch"....
hobbs's user avatar
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5 votes
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How did LADEE and LDRC measure it's distance from Lunar orbit to Earth to 1 centimeter accuracy using optical communications?

In case of optical communication we don't deal with electromagnetic waves that are collected in an antenna at a ridiculously low power level, are amplified by many orders of magnitude and then need to ...
asdfex's user avatar
  • 15.1k
4 votes
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How does a three-way doppler shift measurement work?

Three-way Doppler tracking was developed for when the spacecraft (specifically Voyager) is so danged far away, that by the time the round trip signal gets back to Earth the original transmitting ...
Mark Adler's user avatar
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4 votes
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How does a third DSN station serves as a “relay” to tie-together observations by two other stations doing VLBI?

Very-Long Baseline Interferometry is interferometry with telescopes that physically distant. The observation data is recorded locally, and post-observation the data is combined at a central location ...
Ludo's user avatar
  • 14.4k
4 votes

Delay-Doppler maps in space science

The DDM term is mostly used in the GNSS Reflectometry (GNSS-R) scope, but is conceptually equivalent to the radar ambiguity function. In fact, a GNSS-R system can be understood as a bistatic radar, ...
danipascual's user avatar
4 votes

How does Deep Space Network's DSS-14 transmit radar and receive it at (almost) the same time? (monostatic radar)

Supplemental to @hobbs's answer I've found Soar System Radar Group 332F; Communications Architectures & Research Section 332 with these static image and this animated GIF (it runs about ten times ...
uhoh's user avatar
  • 149k
3 votes

Has there ever been an instance of asteroid discovery by radar; seen first by radar rather than being observed after optical discovery?

Partial answer to get things moving. While so far I haven't found an asteroid proper that was first observed by radar, there are at least several examples of objects that were first discovered ...
uhoh's user avatar
  • 149k
3 votes

Analyse the Doppler effect in non-GEO satellites: calculation of Doppler shift ( frequency)

You have a units problem. First, in general, it is a bad idea to use G and M separately, because the accuracy to which they are individually known is much less than the accuracy to which their product,...
Ryan C's user avatar
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3 votes

Satellite Navigation: Measuring Velocity & Position

But how could the position vector of the satellite and also its velocity vector relative to a ground station be calculated/ measured? It can't, or not per se at least. Except for the most ...
uhoh's user avatar
  • 149k
3 votes
Accepted

Have any deep-space spacecraft supported same-band turnaround of Earth-based doppler measurements?

Yes, and yes. The standard Doppler data type on deep-space spacecraft is X-band to X-band, and transmit and receive are on the same antenna. Most deep-space spacecraft only have X-band transceivers. A ...
Mark Adler's user avatar
  • 58.2k
3 votes

What does Cees Bassa's Doppler plot of Chandrayaan 2 show?

The plot shows the raw, received frequency of the signal from the spacecraft. If the output signal from the spacecraft would be of a fixed frequency, we could directly extract the relative velocity ...
asdfex's user avatar
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3 votes
Accepted

3D celestial puzzler; why InSight's two RISE horns point slightly south of east, and north of west?

The two antennas need to point at Earth during morning and evening on Mars. They are oriented in opposite directions so that one can be used in the morning and one in the evening. The science goal ...
asdfex's user avatar
  • 15.1k
3 votes
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How will InSight's RISE antennas end up pointed in the right direction?

The landing systems seem to be the key. In this paper The Rotation and Interior Structure Experiment on the InSight Mission to Mars (Folkner, W.M., Dehant, V., Le Maistre, S. et al. Space Sci Rev (...
karthikeyan's user avatar
  • 4,469
2 votes
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How many solar system bodies have had coherent radio transponders?

How many solar system bodies have had coherent radio transponders? To communicate with other spacecraft or ground systems at Earth, one needs a transponder or transceiver. So I will show an ...
honeste_vivere's user avatar
2 votes

Delay-Doppler maps in space science

The DDM measures both the delay that a reflected signal takes to get back to you and the doppler (frequency) shift of that signal. In your left most figure, what you are looking at is a picture of ...
Michael Stachowsky's user avatar
1 vote

Calculating change to radio signal propagating around via satellite orbits

Answer: According to Uncle Albert, the speed of light “c” will always be measured the same in an inertial frame of reference. So both the prograde and retrograde signals will travel at the same ...
Woody's user avatar
  • 22.1k
1 vote
Accepted

What are the differences (if any) between the techniques of range-rate and delay-doppler measurements?

It's mostly a terminology question and an application question. As you've correctly pointed out, "delay-Doppler" is the term used for radar tracking of uncooperative systems. For cooperative ...
ChrisR's user avatar
  • 6,180
1 vote
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How exactly does TDRSS provide tracking? (Tracking and Data Relay Satellite System)

This is probably a partial answer because I don't understand it that well myself, but the source document is so incredibly detailed that you can probably build a TDRS yourself from it, so I'm going to ...
Organic Marble's user avatar
1 vote
Accepted

Farthest distance to a solar system object that's been determined by spacecraft transponder?

Scientists routinely use the onboard transponders of deep space missions to return signals from the Deep Space Network in order to determine their distance from earth. This is briefly described in ...
Carlos N's user avatar
  • 4,454
1 vote
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Farthest distance to a solar system object that's been measured by radar?

According to the list at Wikipedia's article on Radio Astronomy, the furthest object that's been measured was probably Saturn's rings; Titan may have been further, depending on where in its orbit it ...
Mark's user avatar
  • 15.3k
1 vote
Accepted

What are monostatic radar observations, and how will Deep Space Network's DSS-13 be used to observe asteroid 1999 WK4's flyby of Earth?

Monostatic just means the transmitter and receiver are in the same place (DSS-14), as opposed to bistatic radar where they are separate (DSS-13 transmitter, Green Bank receiver). No klystron means ...
Hobbes's user avatar
  • 128k
1 vote
Accepted

Is 2012 TC4 part of the Near-Earth Object Human Space Flight Accessible Targets Study?

It is an NHATS object. I found it on there but first I had to select 'Use Unconstrained Settings'. The default view restricts on some parameters. DeltaV is over 10 km/s. On question over the ...
Peter Thomas's user avatar
1 vote
Accepted

Is delay-doppler radar imaging of NEO asteroids possible only if it spins fast enough?

note: After two years of no answer, I've decided to answer this myself. Please feel free to answer if you'd like to contribute something further! Is delay-doppler radar imaging of NEO asteroids ...
uhoh's user avatar
  • 149k

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