Rosetta blog: Rosetta and Philae: Searching for a good signal

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After 7 months in hibernation on a aspect of Comet 67P/Churyumov-Gerasimenko, Rosetta’s lander Philae communicated with Earth around a orbiter on 13 June. Since then, 7 durations of tie have been arguable between a orbiter and lander, though all have been intermittent. One of a pivotal issues being worked on is to adjust Rosetta’s arena to see either a some-more arguable communications couple can be determined with Philae. This news describes a standing of those efforts as of 26 June, and has been prepared with inputs from ESA’s Rosetta Science Ground Segment group during ESAC and a moody control group during ESOC, along with a Lander Control Centre during DLR.

Credits: ESA-C.Carreau

Artist sense of Rosetta transmitting a vigilance to Earth. Credits: ESA-C.Carreau

When have contacts been made?
Confirmed contacts between Rosetta and Philae have been done on 13, 14, 19, 20, 21, 23, and 24 June, though were few during those hit periods. For example, a hit on 19 Jun was fast though separate into dual brief durations of dual mins each. Conversely, a hit on 24 Jun started during 17:20 UT (on house Rosetta) and ran for 20 minutes, though a peculiarity of a couple was really sketchy and usually about 80 packets of telemetry were received. Prior to this, on Tuesday, 23 June, there was a 20-second contact, though no fast couple was determined and hence no telemetry information were received.

How frequently do Rosetta and Philae try to make contact?
Comet 67P/C-G rotates with a 12.4 hour generation and so Philae’s plcae is not always manifest to Rosetta. Roughly speaking, there are dual opportunities for hit between a dual booster any Earth day, though their generation depends on a course of a transmitting receiver on Philae and a plcae of Rosetta along a arena around a comet. Similarly, as a comet rotates, Philae is not always in object and so not always generating adequate energy around a solar panels to accept and broadcast signals. At a moment, a likely hit windows change between a few tens of mins and adult to 3 hours. During these hit windows, a ideal conditions would be that a powered-up Philae hears Rosetta’s job vigilance and responds by substantiating a couple behind to a orbiter, afterwards transmitting a information stored on-board around that link.

Why do we caring about a fast connection?
Data are stored in dual mass memories on-board Philae, and in method to download a information in a many fit approach possible, a fast ‘call’ generation of about 50 mins is desired. It can take around 20 mins for a information to be dumped from any one to a Rosetta orbiter, and additional time is indispensable to endorse that a fast couple has been acquired in a initial place, and also for uploading new commands.

Artist sense of Philae on a aspect of 67P/C-G. Credit: ESA/ATG medialab

Artist sense of Philae on a aspect of 67P/C-G. Credit: ESA/ATG medialab

Can a lander still be operated with brief communications links?
Yes, though this conditions is not ideal given it has an impact on a altogether time accessible to perform systematic operations in a prolonged term. That’s given any time a new scholarship method was initiated, it would take longer to get a amassed scholarship information behind and giveaway adult on-board storage before new commands could be uploaded and subsequently executed.

What competence be inspiring a couple from a lander’s indicate of view?
A series of factors per a lander’s stream standing competence minister to a peculiarity of a communications links celebrated so far. These include:

  • Lander energy availability: a orbiter needs to be drifting beyond a lander’s position when a lander is ‘awake’, that is, when it is generating adequate energy to have a receivers and conductor switched on.
  • Lander plcae and orientation: a course of a lander on a aspect of a comet determines how a receiver settlement is projected into space, and a imperishable topography immediately surrounding Philae can also crush that receiver pattern.
  • Lander health status: errors in a several on-board units could also impact a chances of creation a fast link.

What competence be inspiring a couple from a orbiter’s indicate of view?
Equivalently, there are a series of parameters associated to a orbiter that could be conversion a peculiarity of a communications couple celebrated so far:

  • Distance to a comet: a strength of a vigilance perceived by a orbiter diminishes as a block of a stretch between a orbiter and a lander, and so a chances of a fast couple are reduced if Rosetta is too distant from a comet.
  • Trajectory of a orbiter: to make a link, a receiver settlement of a lander contingency overlie with that of a orbiter, and given a constraints set by a lander receiver pattern, certain trajectories of a orbiter around a comet will be some-more effective during saying a ‘clean’ lander vigilance than others.
  • Pointing of a orbiter: a accurate course of a orbiter in space plays a role, given if a dedicated, non-steerable receiver used to promulgate with a lander is not forked directly during a comet, a strength of a vigilance perceived from a lander will be reduced. Some scholarship observations being done by Rosetta need a orbiter to be forked off a nucleus, though stairs are being taken to equivocate that conditions during intensity contacts with Philae.

Can any of these factors be changed?
Until a fast couple is achieved between a orbiter and a lander and new commands uploaded, it is apparently not probable to try and ‘tune’ a parameters on-board a lander. Thus, benefaction efforts are focused on improving a factors associated to a orbiter. However, this is not straightforward, as a booster operations group contingency keep a reserve of a orbiter as their top priority during a time when a comet is apropos some-more and some-more active.

Processed NAVCAM picture of Comet 67P/C-G taken on 15 Jun 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

Processed NAVCAM picture of Comet 67P/C-G taken on 15 Jun 2015. Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0

How tighten can Rosetta get to a comet and still sojourn safe?
In method to navigate around a comet, Rosetta uses a star trackers to establish a course in space, and so keep a instruments and high benefit receiver forked in a right directions. However, in a dry sourroundings of a comet, particular dirt particles can impersonate stars, creation it formidable for a star trackers to work effectively. If a star trackers are incompetent to establish a spacecraft’s orientation, it will go into protected mode, as gifted during one of a Mar tighten fly-bys of a comet. In a misfortune case, hit with Earth competence be lost, that would lead to a booster entering an unconstrained mode that could take days or weeks to redeem from.

The increasingly-active sourroundings of Comet 67P/C-G is proof to be dustier than designed for when Rosetta was built and so given March, a booster has been drifting at safer distances of roughly 200 km from a comet to avoid similar issues occurring. It has also been altered into a supposed ‘terminator trajectory’ around a comet, also directed during shortening a impact of a dry sourroundings on a star trackers.

The booster operations group are solemnly circumference Rosetta closer to a comet in this terminator trajectory, closely monitoring a opening of a star trackers in ‘continuous tracking mode’, and formulation a arena for a days ahead. At a moment, Rosetta is following a arena intrigue that allows it to come as tighten as 165 km from a comet, and there are signs that dirt division is apropos an emanate again. A stratagem designed for Saturday morning will pierce a booster to 160 km by 30 Jun and a group will consider a star tracker opening during that time in method to establish if even closer orbits are possible, or if Rosetta needs to be altered serve divided again.

How is a arena being changed?
The stream terminator arena of Rosetta has it drifting over a range between comet day and night. The categorical change that can be done within this intrigue is to a embodiment of a belligerent lane of a circuit on a aspect of a comet. This is now being stepped down from +55 degrees (on 24 June) to –8 degrees (on 26 June), with a improved peculiarity vigilance between Rosetta and Philae being rescued during reduce latitudes. For comparison, only after alighting in Nov 2014, Rosetta was drifting over latitudes of +15 to +25 degrees. In a entrance week, a latitudes will solemnly be stepped behind adult again from –8 to +50 degrees, with a clever comment being done of vigilance strength during low latitudes again.

How prolonged is it going to take to solve a situation?
This is a really dynamic, real-time process, and so it is tough to envision when a fast couple competence be done between Rosetta and Philae. The goal teams are operative on a short-term arena formulation schedule, that is updated any Monday and Thursday morning. Changes to Rosetta’s arena are done depending on a latest information with regards lander communications and a opening of a orbiter’s star trackers in a days between any preference point. In addition, member from ESA’s Rosetta team, a Lander Control Centre during DLR in Cologne, and a Lander Science Operations and Navigation Centre during CNES, Toulouse plead daily a latest standing of any lander communication events.

We will keep we posted as serve information becomes available.

Source: Rosetta blog