Forum Replies Created
-
Posts
-
I wonder what power level they used for their “interstellar shout”. DSS-43 has the capability to go to 400kW at S-band although I don’t think that has ever been used. Normal command uplinks are done at 70kW so they may have turned the wick all the way up for this. A 2-deg antenna offset is a loss of around 6dB so that would imply they would need nearly all of the 400kW to restore the link margin. Not much technical info on the NASA report though:
https://www.jpl.nasa.gov/news/nasa-mission-update-voyager-2-communications-pause
I’d put in the distance from memory. It is actually “only” 134au so that increases the angle a bit but not much. Sorry about that!
Yes, sending commands to Voyager 2 is a lot harder than receiving the telemetry. The spacecraft receiver is a bit unstable due to a capacitor failure and the noise temperature is high since the antenna is effectively looking at the Sun. The only ground station in the DSN that can command Voyager 2 is DSS-43 at Canberra. This has a huge 400kW power amplifier (the other 70-m stations have 20kW) but there are all sorts of restrictions on its use. I wouldn’t want to be a bird in the beam of that thing when it is transmitting at full power.
If you want some fun bedtime reading have a look at these links:
https://descanso.jpl.nasa.gov/DPSummary/Descanso4–Voyager_new.pdf
http://deepspace.jpl.nasa.gov/dsndocs/810-005/101/101E.pdf
https://deepspace.jpl.nasa.gov/dsndocs/810-005/relnotice49.pdf
https://space.stackexchange.com/questions/18956/has-dss-43-ever-been-used-in-high-power-mode-20-kw-for-an-emergency-situationThe spacecraft antenna pointing would be based on on-board sun and star tracker data so I assume they have a stored ephemeris for offsetting the pointing from the Sun to get peak gain towards the Earth. Voyager 2 is currently around 160au away so the Earth is always within 0.35 deg of the Sun anyway but this is what will happen in mid-October when it executes its next pointing update.
Voyager 2’s antenna is a 3.7-m diameter paraboloid and at S-band (2 GHz) a 2 degree pointing error would imply a link budget loss of around 6dB which is huge. It is probable that the 70-m DSN antenna at Canberra will be able to detect and lock to the residual downlink carrier but unlikely that they will be able to decode any data. They could decide to array lots of antennas to improve the downlink SNR but the main problem would be getting commands up to the spacecraft to reset the pointing.
Given the low science return from Voyager now it is probably easiest just to wait until the next antenna pointing update.
I got it at twilight this morning after a night of comet imaging. It was on its way out to apogee at a range of 120,000 km or so.
According to Horizons it should have been at 00 10 42.42 -04 00 27.0. The attached shows it a bit northeast of that but it looks as if the Horizons ephemeris is pretty good. This is a 60s exposure so the magnitude is meaningless since the image was trailed.
Attachments:
Robin – That’s really impressive! Alan’s talk was really fascinating. I’m in awe of the precision of modern observational astronomy. I had no idea that we had directly detected comets around other stars through photometry or that we had seen variable absorption lines in high-resolution spectra which are inferred to be comets in the circumstellar disk of beta Pictoris. I need to do a lot more reading on this.
A fantastic day at the National Maritime Museum yesterday. We had over 100 people attend for a day of great talks about comets. My thanks to all the Flamsteed team and the people at the NMM who made the meeting possible, Dr. Greg Brown who gave us a great planetarium show, the speakers who were uniformly brilliant and to the audience who were really engaged and asked lots of excellent questions. My thanks also to Gill and Roger Perry who spent the day videoing the event. We’ll put the video online when it is ready.
If you did attend yesterday I hope you enjoyed the day and got home OK. I’m clearly biased since I think comets are the most interesting objects in the universe but with the direct observation of exocomets I think I can now extend my section’s reach to other star systems.
Thanks for that. ESA are tracking it and it is a shame that they haven’t publicly released any trajectory information. I’m not aware of any optical observations yet but it has been close to the Moon in the sky and it is at a far south declination. Once the Moon is out of the way I expect it will be picked up. I’ve been keeping an eye on NEOCP to see if any of the surveys get it.
ESA Ops did a small (2.1 m/s) trajectory correction the day after launch which implies that the Falcon 9 upper stage injection was very good. As far as I can tell everything is fine with the spacecraft.
Yes, checking that your train actually exists is always good advice at the moment! Hopefully the work to rule won’t have a major impact.
We have over 90 people registered so it should be a good day. We’ll probably end up in the Trafalgar after the meeting although it will probably be more rammed than usual even for a Saturday night in Greenwich. The Kaiser Chiefs are playing at the Naval College at 8:30pm. No doubt “I predict a riot” will be in the set but hopefully there won’t actually be one.
Launch on Falcon 9 looked to be perfect and acquisition of signal happened on time at the New Norcia ground station in Australia. As I write this the spacecraft is being tracked and commanded by the 35-m antenna at Cebreros, just outside of Madrid. I haven’t managed to find an ephemeris but it must be pretty close to the Moon in the sky since the shadow of the subreflector (equivalent to the Cassegrain secondary) is almost on top of the beam waveguide entrance aperture (the hole in the main dish). A live image of the antenna is here:
https://tethys.ejr-quartz.com/cebreros/cebreros.jpg
Attachments:
At perihelion the Earth’s umbra extends around 1.4 million km away so, as Dominic says, you would only see an annular eclipse from L2 which is around 1.5 km outward from the Sun. Eclipses are really bad things for spacecraft which rely on solar arrays for power so the outbound trajectory will avoids the Earth’s shadow wherever possible. L2 is gravitationally unstable and so spacecraft don’t actually sit at the Lagrange point itself but orbit in a halo around it with relatively frequent small thruster burns to keep them on station. We’ll have another opportunity to watch a spacecraft heading out to L2 when ESA’s Euclid gets launched on a Falcon 9 at the start of July.
Back on topic though. Could those additional items be added to the forum topics list?
Robin. Thanks for that. A very interesting paper.
The Sony IMX455 is certainly a very nice sensor for astronomy. Here’s what you can do with it if you couple it to a Celestron RASA 11 and have very dark skies:
https://www.spaceobs.com/Blog-de-Alain-Maury/MAP-historique-et-description
Nick.
Robin – That was a very interesting programme. Some of the BBC’s science output is still pretty good. Here’s my lightcurve so far taken from the BAA database. Hopefully this good weather will continue so we can keep monitoring it.
-
This reply was modified 2 years, 2 months ago by
.
-
This reply was modified 2 years, 2 months ago by .
Attachments:
It’s now (2023-05-21 22h UT) around 11.3 so still brightening quickly. The total integrated magnitude of M101 is around 8.0 so this one object is currently 5% of the brightness of the entire galaxy.
That’s interesting. The latest non-detection on TNS is from ATLAS at 2023-05-18 10:17 UT when they reported > 20.5.
I imaged it earlier this evening (May 20/21) and it has risen to around mag 12.0 now.
Attachments:
It’s rather hazy in Chelmsford but here but here is an unfiltered image of the SN.
Attachments:
