13 votes

Why was the 100m Green Bank dish needed together with DSN's 70m Goldstone dish to detect Chandrayaan-1 in lunar orbit?

The explanation has to do with the operation of the radar transmitters and the round trip light travel time. It takes about 3 seconds for a radar pulse to travel from the Earth to the Moon and back. ...
12 votes
Accepted

What is the current record for the farthest detection of a "dead" spacecraft?

There are two potential candidates that I'm aware of. The first is J002E3, which is believed to be the Apollo 14 Saturn 5 upper stage. At the time of detection, it was orbiting Earth between 1-2 ...
  • 120k
9 votes
Accepted

How do ultra-stable oscillators for spacecraft work?

The material depended on the mission but was usually quartz, and the stability is insane. The development of Ultra-Stable Oscillators (USOs) is ongoing (see here and here). NASA/the ESA have used ...
8 votes

What are the pros and cons of Doppler radar versus Doppler lidar?

NOTE: This discusses autonomous car sensors but the same physics will apply to any longwave vs. shortwave sensor comparison (cost being the wildcard) An interesting parallel is Tesla Inc.'s decision ...
7 votes
Accepted

Why does DSN sometimes uses two dishes at the same time to receive Voyager-1?

If you look at the "more detail" section of the DSN status web page, you'll see that 25 and 26 are operating in "array mode". With two antennas receiving, twice as much incoming signal is being caught,...
7 votes
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Help understanding BepiColombo's weak capture at Mercury's L1 and need for delta-differential one-way range measurements

"Weak capture" means that the spacecraft will enter the Mercury's gravitational sphere of influence along a weak stability boundary. These weak stability boundaries are one of the key mathematical ...
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5 votes
Accepted

Why such a large observed doppler shift from Apollo 17 orbiting the moon?

From your link: If the orbit had been perfectly circular at the 128.2 minute period the doppler shift for a simple transmitter would have been = 2287.5 x 1000 x 1.58/300000= ± 12 kHz. For a ...
4 votes
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How could tiny Hagoromo have been seen visually from earth confirming its lunar orbit?

From the NASA Space Science Data Coordinated Archive entry on Hagoromo, The ignition of the Hagoromo deceleration rocket was confirmed by ground observation at 20:04:03 UT. From a few other sites, ...
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4 votes

Why was the 100m Green Bank dish needed together with DSN's 70m Goldstone dish to detect Chandrayaan-1 in lunar orbit?

I know nothing of the activity you're asking about, but I do know something about radar. All the radar systems I've worked with used a single antenna to both transmit and receive. The power of the ...
  • 1,154
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 ...
3 votes
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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 ...
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 ...
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3 votes

How are the Voyagers' thrusters configured in a novel way to minimize accelerations along Earth-spacecraft axis?

This answer is somewhat speculative and relies upon a generous interpretation of what "minimizes accelerations" means. I obtained a three-view drawing of the Voyager from a link in this ...
3 votes

Why was the 100m Green Bank dish needed together with DSN's 70m Goldstone dish to detect Chandrayaan-1 in lunar orbit?

Since the deep space network can perform ranging on spacecraft much farther away (tens of thousands of times farther than the moon) by itself, why was it necessary to use a non-colocated, non-DSN dish ...
  • 122k
2 votes

What are the pros and cons of Doppler radar versus Doppler lidar?

I think you mean to ask the question about LIDAR as used for velocity measurement in spacecraft rather than the LIDAR used in autonomous vehicle. Here, I list some few points relating to both ...
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2 votes

What is the current record for the farthest detection of a "dead" spacecraft?

I can name two other spacecraft, one of which was significantly further away than Rosetta: SOHO (The Solar and Heliospheric Observatory) near L1 (approx 1 million miles from earth). After a gyroscope ...
  • 634
2 votes
Accepted

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 ...
2 votes
Accepted

How have/how will Indian ground stations be used for comms or tracking of deep space spacecraft?

32 meter antenna of IDSN is being used by JAXA and ISRO to study Venusian atmosphere using signals from Akatsuki probe and Radio occultation technique. ISRO is also planning a Venus mission so these ...
  • 1,587
1 vote

Why was the 100m Green Bank dish needed together with DSN's 70m Goldstone dish to detect Chandrayaan-1 in lunar orbit?

This started out as a comment on one of the answers already provided, but it grew much too big to stay that way. There is good reason to collect and process bistatic ranging data even when there is no ...
  • 6,352
1 vote

How are the Voyagers' thrusters configured in a novel way to minimize accelerations along Earth-spacecraft axis?

"Novel" here means in respect to other planetary missions, and also the thruster fuel: the previous missions to the outer planets (Pioneer) were spin-stabilized, and previous missions to the ...
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