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Scott Tilley

Jan 10 • 5 tweets • 3 min read

#TIANWEN1 orbit remains unchanged based on period measurements.
T=25482s,
a=8898km. So no aerobrake test yet.

Neuquén ground station apparently attempted to lock to the spacecraft last night and failed. News reports of orbiter having communications issues. 🧵⬇️

This zoomed in Doppler plot of #TIANWEN1's signal during the anomalous lock attempt from yesterday is depicted below. Neuquén ground station appears to be using uplink Doppler compensation but is out of sync with the actual orbit of the spacecraft. ⬇️

https://twitter.com/nascom1/status/1598529266815160321

Uplink Doppler compensation (UDC) is used by a ground station to place the uplinked signal at the spacecraft at a constant signal. It does this by 'ramping' the signal it transmits to match the 1-way Doppler to the spacecraft. ⬇️

https://twitter.com/nascom1/status/1598529266815160321

During the #TIANWEN1 periareion part of the pass the Doppler changes rapidly and if you wanted to be in lock say to measure range accurately while skimming the Martian atmosphere you run the risk of drifting out the of the spacecraft rx passband. UDC solves this. ⬇️

Normally #TIANWEN1 hasn't been observed to use UDC but they may need it to do the aerobraking test. However, with reports of communications issues this may be challenging the mission controllers. 🛑
spacenews.com/chinas-tianwen…

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More from @coastal8049

Scott Tilley

@coastal8049

Jan 12

I've recently renewed an observing campaign on #TIANWEN1. The orbit hasn't changed so an aerobrake test claimed for late 2022 has not occurred yet. In preparation for observing an aerobraking manoeuvre I thought it would be interesting to study past missions that did one. 🧵⬇️

First a bit a reference of why we believe #TIANWEN1 will conduct an aerobraking test. This all relates to the #TIANWEN3 Mars sample return mission.
spacenews.com/china-aims-to-…

Aerobraking is used to allow a spacecraft to lower its apopasis by using a planet's atmosphere to decelerate the spacecraft as it passes through the tenuous upper atmosphere of the planet at periapsis at just the right altitude as not to cook the spacecraft and max. drag. ⬇️

Read 13 tweets

Scott Tilley

@coastal8049

Nov 13, 2022

The R/B of the Yunhai 1-03 mission appears to have suffered a breakup event. The plane of the orbit is nicely visible in the evening in the Northern hemisphere. Observers could look for debris by observing along the R/B plane and looking early.
OBJECT B [54236, 2022-151B] 🧵

The irony is the satellite Yunhai 1-03 is replacing was itself hit by another satellite. Goes to show you that space junk at these orbital altitudes is not a good thing.
space.com/china-yunhai-1…

Look as soon as possible if you plan too before it disperses too much.

Read 4 tweets

Scott Tilley

@coastal8049

Sep 10, 2022

⚡️WATCHING:

#CAPSTONE appears to be garnering the DSN's attention over the last day or so. Continuous uplinks with no downlink like the anomaly observed after the spacecraft was released post TLI.

She was scheduled for TCM-3 in early September based on statements after TCM-2.

I'm presently tracking #CAPSTONE on X-band and noting no emissions from it over the last few hours.

DSN NOW just updated and most of Goldstone's DSS antennas are now tasked with #CAPSTONE. Even DSS 14.

Read 27 tweets

Scott Tilley

@coastal8049

Aug 27, 2022

https://twitter.com/DegenerateConic/status/1561531340067061762

#ARTEMIS1 observational planning 🧵

Overall visibility of the spacecraft from my ground station location. Elevation above the horizon will be a key factor. As you can see during the early and late stages of the mission Artemis will be low in my sky.

https://twitter.com/DegenerateConic/status/1561531340067061762

Next lets consider the range to #ARTEMIS1 so a model of the expected signal level can be obtained using Free Space Path Loss (FSPL) assumptions. Data is only plotted when Artemis is above my horizon.

The following are estimates of the SNR of #ARTEMIS1's signal in my 1.8m dish using an Equivalent Noise Bandwidth (ENBW) of ~2Hz for my usual SDR setup during the course of the mission. Assumed spacecraft High Gain Antenna (HGA) and the known sensitivity of my system used here.

Read 5 tweets

Scott Tilley

@coastal8049

Mar 19, 2022

MERIDIAN 9 on it's Eurasian apogee.

As you can see here there's legit Russian military traffic here.

Aircraft spotters I make a call for you to pay attention to this 🧵.

MERIDIAN 9, 990MHz transponder narrow data. This type of traffic has been observed for decades on the Molniya-T1 spacecraft too. It is thought to be part of the Russian Strategic Rocket Force's communication system.

https://twitter.com/GDarkconrad/status/1504389947129741313

A call for #OSINT air traffic gurus to see if any Russian aircraft with strange humps on their back are orbiting somewhere over Russia right now. Like RSD79 in this post.