In this blog we will examine the methods used by the European Space
Agency (ESA) to incorporate data collection and management protocols within the
system architecture of the Philae comet lander which landed on Comet 67P/Churyumov-Gerasimenko
November 12th, 2014 (Howell, 2015).
The Philae lander and its mothership, the Rosetta space probe,
was launched from the ESA’s French-Guiana launch facility in 2004. Following a
10-year chase, the Rosetta probe reached Comet 67P and deployed the Philae
lander on mission to determine the comet’s physical structure and composition (ESA,
2014). Unfortunately, the lander’s harpoon anchoring system failed to operate
properly resulting in the Philae coming to rest on the comet’s surface at an
angle. As the lander’s solar panels were unable to provide enough power for the
expected duration of the mission, Philea went silent after 64 hours of
operation and was placed into hibernation (Grady, 2016). Despite this setback,
the lander was still able to transmit a wealth of information about Comet 67P despite
the less-than-perfect landing, a testament to excellent hardware design.
Aboard Philea, the CDMS (Command and Data Management
Subsystem) engineered by the Hungarian SGF Company (SGF Technology Associated
Co. LTD, 2015) was responsible controlling of all of the lander functions.
According to SGF (SGF, n.d.), the CDMS is a modular design that, while on the
comets surface, would collect and execute commands from Earth, send scientific
and lander status to the nearby Rosetta spacecraft for retransmission to
controllers, and control sequencing of the scientific instrument operations.
The CDMS features a common motherboard that supports redundant
sub-units including two DPUs (Data Processing Units), two RTC (Real Times
Clocks), two CIUs (Central Interface Units), two Mass Memory boards, and a
Power Distribution board. SFG states that the primary DPU performs payload
operations while the secondary observes the results. Thus the secondary DPU may
assume payload control in case of primary DPU failure (SFG, n.d.). A journal posted for the 2003 DASIA (Data
Systems in Aerospace) conference (Baksa et al., 2003) describes the DPU as
containing a Harris RTX2010 processor with a 16-bit processor that is
radiation-hardened for space travel. A DPU also contains the program and memory
data sets as well. Communication between system components is controlled by the
CIU through a serial data transmission channel with a data transfer rate of 32 Kbit/s.
System timing is controlled by the RTCs to ensure that critical functions occur
exactly as programmed. The Massive Memory boards are capable of storing huge
amounts of data (exact amount unspecified) garnered from mounted scientific
instruments during the time periods when the lander is in the radio-shadow of
the Rosetta probe. FORTH based software serves the operating system for the
redundant CDMS components which operate in parallel for fault-tolerance, a
critical characteristic for space vehicles which may be out of Earth contact
for long periods of time.
The CDMS is also responsible for establishing data
communication for transmission to Earth. According to NASA Technical Memorandum
2006-214431 (Gwaltney & Briscoe, 2003), the Rosetta mission utilized the
European-developed SpaceWire protocol. The SpaceWire method permits a large
number of devices to be networked that can communicate with each other at
speeds of up to 400MB/s. This data transfer protocol was an ideal choice for
the Rosetta mission where a low-powered lander was required to transmit bursts
of data to the mothership over specific time periods (i.e., when the Philae and
the Rosetta spacecraft were in position to communicate) for retransmission to
Earth.
In summary, the Philae lander demonstrated the vital
importance of well-designed data management systems and redundant system
architecture supported by robust hardware and software. Despite enduring 10
years of space travel, and then literally bouncing off
the surface of comet and landing awry, Philae was able to meet 90 percent of
its scientific goals (Gibney, 2014). A truly remarkable accomplishment
following a long and arduous journey to explore a little known and primeval
relic from the dawn of the creation of our solar system.
References:
ESA. (2014). The Rosetta Lander. Retrieved from
http://www.esa.int/Our_Activities/Space_Science/Rosetta/The_Rosetta_lander
Gibney, E. (2014). Philae’s 64 hours of comet science yield rich data. Retrieved from
http://www.nature.com/news/philae-s-64-hours-of-comet-science-yield-rich-data-1.16374
Grady, M. (2016). Farewell to Philae as Rosetta Probe goes
into 'Eternal Hibernation'. Retrieved from
https://www.theguardian.com/science/2016/feb/12/farewell-philae-rosetta-probe-goes-into-eternal-hibernation-comet-67p-churyumov-gerasimenko
Gwaltney,
D. A., & Briscoe, J. M. (2003). Comparison
of Communication Architectures for Spacecraft Modular Avionics Systems.
Retrieved from http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060050129.pdf
Howell, E. (2015). Wild, History-Making Comet landing by Philae
Probe recreated in Video. Retrieved from
http://www.space.com/31129-philae-comet-landing-rosetta-video.html
SFG. (n.d.). Command and Data Management Subsystem (CDMS)
of the Rosetta Lander (Philae). Retrieved from
http://www.sgf.hu/newsgfweb3_005.htm
SGF. (n.d.). Command and Data Management Subsystem (CDMS)
of the Rosetta Lander (Philae). Retrieved from
http://www.sgf.hu/newsgfweb3_005.htm
SGF Technology Associated Co. LTD. (2015). Welcome to our Web Site. Retrieved from
http://www.sgf.hu/
Very interesting Mark. I can see the application of deep space storage sensing technology being applied directly to unmanned systems here on Earth.
ReplyDeleteThe current distance from comet 67 P to the Sun is causing a substantial decrease in data rates. The comet has moved further from the Sun in its orbit, the lander is going to have to survive the extreme cold temperatures of space, with almost no guarantee that it will get enough sunlight to power itself. This could make all of the sensors of no use. The chances that Philae will ever communicate are remote.
ReplyDeletethat is so impressive that we could still land on the comet and gather data even when the harpoon failed and it was at an angle. the data transfer rate was impressive and having the systems protected from the radiation was very creative
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