Hopefully everyone had a chance to see at least a part of Monday’s solar eclipse, which is certainly one of this year’s space topics highlights. The next big thing is happening in mid-September — the death plunge of the Cassini spacecraft into the ringed planet Saturn (stand by for a very special interview about it!).
Nestled in between these giants of publicity and media darlings is the last of the third generation TDRS satellites (pronounced Tee-Driss). Except for their launch the TDRS satellites don’t make the news a lot. TDRS stands for Tracking and Data Relay Satellite — essentially the knee joint between some celebrated spacecraft and a ground station. Yeah — it’s not even a clever acronym, right? Spacecraft send their signals to a TDRS satellite, and they pass it on to a big satellite dish on the ground, say, in New Mexico or Guam (indeed, there’s more to Guam than military assets and evil-eyeing by megalomaniac dictators). Unlike the Deep Space Network (DSN), which is mostly concerned with spacecraft beyond Earth’s moon, the TDRS crowd deals with Earth-orbiting science satellites.
The TDRS series has three levels — the first generation is way past its intended life span, yet two of them are still limping along up there. They are joined by two more second generation satellites (also near retirement age), and three third generation vehicles, plus several decommissioned ones in special “parking orbits.”
All TDRS satellites operate in geosynchronous orbit — some 22,300 miles up, where it takes them exactly 24 hours to circle the Earth once. By comparison, the International Space Station (ISS), which is only a couple of hundred miles up zips around our fair planet once every 90 minutes, so that gives you a good idea just how far up the TDRS crowd hangs out. From the viewpoint of an observer on Earth a satellite that is in geosynchronous orbit at the equator appears to stand still in the sky. And that’s precisely what makes them so useful for data relay — their ground stations always know where they are and can keep their dishes pointed in the right direction!
The equatorial synchronous orbit is a busy zone up there — this is also where all the commercial communications satellites ply their trade, so you can get your TV, rural internet coverage and other goodies. However, you’re not going to have much direct contact with the new kid on the block TDRS-M, which was launched last weekend. TDRS-M will pick up communications from the ISS, the Hubble Space Telescope and other low-Earth orbit science platforms. So indirectly TDRS-M is going to play a huge role in your life if you’re even a tiny bit of a space nerd. … If you love colorful Hubble photos, or you follow the denizens of the ISS on Twitter, you will benefit from TDRS-M very soon.
Getting into geosynchronous orbit is no easy feat: it takes a honkin’ big rocket to get you that far out. And since there are few places right on the equator to launch a rocket you’ll most likely go into a highly elliptical angled orbit first, which will then be circularized and lined up over a period of months or more. During this adjustment phase TDRS-M will test all of its equipment and fine-tune everything, and after about five months it will end up somewhere over the Atlantic and begin its regular service.
TDRS-M is a workhorse, and it looks like one: a big boxy thing with two giant mesh dish antennas on either side and one in the middle, and solar panels for power generation. As ungainly as it may look it is nonetheless one of the most successful designs up there — the 76thspacecraft to fly in this configuration attests to the usefulness of its layout.
So next time you read a tweet from the ISS or ooh and aah over a Hubble photo, send a mental thank you note to the TDRS satellites and the invisible handshake in the ether that happens during a communications relay process.
Learn more about the TDRS satellites at http://ift.tt/2ldRrSB
Beate Czogalla is the Professor of Theater Design in the Department of Theatre and Dance at Georgia College & State University. She has had a lifelong interest in space exploration and has been a Solar System Ambassador for the Jet Propulsion Laboratory/ NASA for many years. She can be reached at our_space2@yahoo.com.
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