In my previous post, I spoke about the opportunity to take images of the Moon and Earth using the Inory eye camera on DSLWP-B during the first week of June. All the tentative plannings for programming the image taking and downloading the images listed in that post were eventually made final, so the observation runs have been done without any modifications to the schedule.
On June 3, a series of 9 images with 10 minutes of spacing was taken starting at 03:05 UTC. This gives a nice sequence of the Earth hiding behind the Moon and reappearing. One of the images was partially downloaded during the same 2 hour activation of the Amateur payload on June 3. Several of the remaining images were downloaded between June 4 and June 6. On June 7, the station of Reinhard Kuehn DK5LA, which is normally used as the uplink station, wasn’t available, so a single image outside of the Moon series was downloaded using Harbin as uplink station.
This is a report of the images taken and downloaded during this week.
Yesterday, Wei Mingchuan BG2BHC sent an email to the team of DSLWP-B collaborators saying that the first week of June would give good opportunities both to take images of the Moon and Earth (as it has been done in other occasions) and to perform VLBI sessions involving Dwingeloo, Shahe, Harbin, and perhaps Wakayama University, which has a 12m dish. Here I show the preliminary plan proposed by Wei and a few graphs useful for camera and VLBI planning.
Since I wasn’t going to be at home at that time, I programmed my computer to make a recording for later analysis. I recorded 4MHz of spectrum centred at 10367.5MHz using a LimeSDR connected to the LNB that I use to receive QO-100. The recording was planned to be 30 minutes long starting at 20:01 UTC, but for some reason only approximately 27 minutes were recorded.
This kind of events can be used to measure Moon noise and receive 10GHz EME signals. This post is an analysis of my recording, looking at these two things.
Last Sunday, Julián Fernández EA4HCD, released a high altitude balloon carrying a LoRa payload as a preliminary test for the FossaSat-1 pocketqube that he is devolping with Fossa Systems. You can see a video of the release in this tweet. The balloon was launched near Madrid, and burst at an altitude of approximately 24km, having travelled some 180km southeast.
The payload had two transmitters: An SX1278 LoRa transceiver transmitting at 434.5MHz with 10mW alternating between LoRa and RTTY, and an 868MHz 25mW LoRa transceiver that was received on The Things Network. Simple groundplane 1/4-wave monopole antennas were used.
I went to the countryside just outside my city, Tres Cantos, and set up a station to record the transmissions on 434.5MHz. The station consisted of a 7 element yagi by Arrow Antennas, set in vertical polarization and placed on a camera tripod on the roof of my car, and a FUNcube Dongle Pro+. This is a brief analysis of the recording.
The first Amateur VLBI experiment with DSLWP-B was performed on 2018-06-10. In that experiment, the 250baud GMSK beacons at 435.4MHz and 436.4MHz were recorded in the 25m PI9CAM radiotelescope in Dwingeloo, The Netherlands, and a 12m repurposed Inmarsat C-band dish in Shahe, Beijing. These synchronized recordings were processed later to obtain delta-range and delta-velocity measurements. Due to the low baudrate, the noise of the delta-range measurements was quite high, on the order of 20km. Since the beacons were short transmissions of 15 seconds, making accumulated phase measurements was not possible.
Another Amateur VLBI experiment was performed on 2018-11-21. The novelty of this experiment was that 500baud GMSK SSDV transmissions were made on 436.4MHz. These long transmissions, lasting around 30 minutes each, allow us to make accumulated phase measurements. Also, the higher baudrate reduces the noise in the delta-range measurements. Another novelty was that a third station, the Harbin Institute of Technology Amateur Radio Club BY2HIT groundstation also joined the experiments, so observations from three stations are available.
This post is an account of the results I have obtained processing the observations from 2018-11-21.
A few days ago, I spoke about the future impact of DSLWP-B on the lunar surface, which will happen in the far side of the Moon around the end of July, and how the spacecraft could be manoeuvred to make the impact point fall on the near side of the Moon instead, so that it can be observed from Earth.
Philip Stooke made a very good remark in the comments saying that the impact might have been planned on the far side of the Moon deliberately in order to avoid Apollo landing sites and other heritage sites. This is a very valid concern. By all means, the crash should be planned to avoid disturbing heritage sites or other areas of specific interest.
On April 28, I got together with a few Spanish radio Amateurs to perform some experiments. One of the things we did was an angle of arrival experiment in the 145MHz Amateur band. The ultimate goal of the experiment was to be able to measure the angle of arrival of meteor reflections of the GRAVES radar at 143.05MHz. However, we also recorded a few other signals, such as the Amateur satellite band at 145.9MHz (intended to perform calibration of the setup) and the APRS terrestrial signals at 144.8MHz.
In my last post, I spoke about the future lunar impact of DSLWP-B on July 31. Edgar Kaiser DF2MZasked over on Twitter if the impact would be visible from Earth. As I didn’t know the answer, I have made a simulation in GMAT to find this out.
The figure below shows the orbit of DSLWP-B between July 28 12:00 UTC and the moment of impact, on July 13 14:47 UTC. The orbital state used for DSLWP-B is the 20190426 tracking file from dslwp_dev. The reference frame is arranged so that the +X axis points towards the Earth, and the Y axis lies on the Earth-Moon orbital plane. As we can see, unfortunately, the impact will happen on the far side of the Moon, where it is not observable from Earth.
However, it is possible to arrange a manoeuvre to modify the orbit slightly and make the impact point fall on the near side of the Moon, where it is visible from Earth. In the previous post we observed that, ignoring the collision with the lunar surface, the periapsis radius would continue to decrease after July 31, until reaching a minimum value in January 2020.
Therefore, it is possible to raise the periapsis radius slightly in order to delay the collision approximately half a lunar month, so that the periapsis faces the Earth at the moment of impact. The delta-v required to make this manoeuvre is small, as the adjustment to the orbit is subtle.
For instance, performing a prograde burn of 7m/s at the first apoapsis after July 1 delays the collision until August 13, producing an impact in the near side of the Moon. The resulting orbit can be seen in the figure below, which shows the path of DSLWP-B between July 28 and the moment of impact.
Adjusting the delta-v more precisely would make it possible even to control the time of the impact, so as to guarantee that the Moon will be in view of the groundstations at China and The Netherlands when the collision happens. However, this adjustment requires a very precise delta-v and is quite sensitive to the orbital state, so perhaps it is not feasible without performing a precise orbit determination and maybe some smaller correction manoeuvres following the periapsis raise.
Another possible problem that can affect the prediction of the impact point are the perturbations of the orbit caused by the lunar mascons, which can be noticeable when the altitude of the orbit starts getting small, and which haven’t been considered very carefully in this simulation (the non-spherical gravity of the Moon was only simulated up to degree and order 10).
The GMAT script used for this post can be found here.
On January 24, the periapsis of the lunar orbit of DSLWP-B was lowered approximately by 500km, so that orbital perturbations would eventually force the satellite to collide with the Moon. This was done to put an end to the mission and to avoid leaving debris in orbit. It is expected that the collision will happen at the end of July, so there are only three months left now for the DSLWP-B mission. Here I look at the details of the deorbit.
There is a saying that goes like “even a broken clock is right twice a day”. In the same spirit, even a QO-100 station, which is installed with a fixed dish aiming to Es’hail 2, can sometimes be used for observing the Moon, as it happens to pass in front of the beam.
My station has a 1.2m offset dish with a GPSDO disciplined LNB. There are a few things that can be done when the Moon passes in front of the beam of the dish, such as measuring moon noise (though the increase in noise is only of around 10K with such a small dish), or receiving the 10GHz EME beacon or other EME stations. Therefore, it is interesting to know when these events happen, in order to prepare the observations.
I have made a simple Jupyter notebook that uses Astropy to compute the moments when the moon will pass through the beam of the dish (say, closer than 1º to the position of Es’hail 2 in the sky). Of course, the results are highly dependent on the location of the groundstation, so these are only valid for my groundstation and perhaps other groundstations in Madrid. Other people can run this notebook again using their data.
It turns out that each year the Moon passes roughly a dozen times in front of the dish beam. The next observation for me is on May 16. The separation in degrees between the centre of the Moon and the centre of the dish beam can be seen in the figure below.
This notebook can be used to plan for transits of other astronomical objects, but besides the Moon and the Sun, there are no other objects that are visible at 10GHz with a small dish. It is well known when the Sun passes in front of the beam, since this disturbs communications with GEO satellites. This is called Sun outage and it happens during a few days around the equinoxes (a few weeks sooner or later, depending on the latitude of the station). On the other hand, the transits of the Moon happen throughout the whole year, at rather unpredictable moments, so I think this notebook is quite useful to plan observations.