It doesn't seem to be widely known, but, China appears to be
planning to send a lander to Mars in 2016.
As with most Chinese space projects, hard facts are scarce. A presentation gives some sketchy details of
the mission. From
this report we are able to glean the general outline of the mission and the
fact that China actually has plans for a Mars exploration program.
Figure 1. Chinese orbiter and lander aeroshell.
This diagram shows the lander aeroshell and the orbiter that
will carry it to Mars (Figure 1). Upon arrival at the Red Planet, the
orbiter/lander combination will enter a capture orbit while still attached to
each other, as was done during the Viking missions. The dual craft will then enter a lower orbit
from which the lander will descend to the surface (Figure 2). As shown in the diagram, the orbiter will
serve as a relay for the lander before it maneuvers into a lower science
orbit.
Figure 2. Chinese plan to land from orbit
The Entry, Descent and Landing (EDL) sequence is shown
in Figure 3. Not much detail is revealed, but in brief,
it seems to be a typical EDL sequence followed by most Mars landers. This report indicates that the landing will
be semi-soft. The only clue as to what
the lander may look like is shown in a cut-away diagram of the aeroshell. (Figure 4) Apparently, it will be battery-powered, with
a 3 – 5 day life on the surface. The
lander will have a mass of only 40 – 100 lb.
This will leave little capability for any science instruments. The available diagrams do not clearly
indicate whether there will be a separate lander within the aeroshell, or if
the aeroshell structure itself will double as a lander.
Figure 3. Chinese entry, descent, and landing sequence.
Figure 4. Chinese Mars demonstration lander.
In addition, the report indicates 3 candidate landing sites
for this mission. They are all at about
45 degrees N latitude, which may be
dictated by the orbit of the carrier spacecraft. All 3 sites are targeted for the plains of
Mars possibly to find terrain that is as amenable as possible to a safe landing (Figure 5).
Figure 5. Possible Chinese landing sites
Even though this may
be a simple hard lander, it would still be a great leap forward for China's
space program. This report also
outlines a long-term Mars program that includes a Rover and Sample Return. (Figure 6) The unmanned Chang'e lunar program has shown
that China is willing, and able, to follow through on fulfilling long-range
plans. If it does the same with its
proposed Mars program, then we could see another major player in the
exploration of the Red Planet.
Figure 6. Proposed Chinese Martian exploration program.
In fact, China may be
laying the groundwork for its Mars program in the Chang'e program. Later this year, the Chang'e-3 mission should
deliver a rover to the Moon's surface.
In 2017, the Chang'e-5 spacecraft is set to return samples from the
Moon. In preparation for that mission,
the Chinese have recently announced that they will conduct an Entry Vehicle
test flight in 2015. This qualification
mission will fly a copy of Chang'e-5's entry capsule attached to a bus derived
from the Chang'e-2 lunar orbiter. The
mission profile is not clear, but it can be imagined that the bus/capsule
combination will fly out to at least the Moon's orbit before returning to the
Earth. This will allow the capsule's
thermal protection system to be tested at velocities encountered by spacecraft
returning from the Moon or Mars.
As to whether the
2015 bus/capsule spacecraft will perform a return from lunar distances without
approaching the Moon (as in the Soviet Zond 4 mission) or whether it will loop
the Moon (as with the Soviet's Zond 5) is an open question. Not only will this test the Chang'e-5's
capsule design, but it will serve as a pathfinder for China's 2016 Mars EDL
capsule and future Martian sample-return craft.
The 2018 Mars window will see the launch of the joint
ESA/Roscosmos Exomars 2018 rover/lander.
A recent status report has revealed new details of the Russian Descent
Module. This lander is set to deliver ESA's rover to
the surface of Mars. The report shows
the Russian surface platform to be a 4-legged (or 3-legged) rocket-powered
lander. This is very similar to the
design of the Viking and Phoenix soft-landers, as well as the descent stage of
the Soviet advanced Luna landers, e.g., Luna 16.
The design of the
Russian lander appears to be somewhat fluid .
In an earlier post , Van showed a version of the lander that appears in
several illustrations from this newest report.
(Figure 7 to 10) The lander option in the upper-right of this
diagram is especially intriguing. It
shows a descent module with legs that are folded upward after landing. This would lower the platform so that the
rover could more easily egress from the lander.
Figure 7. ExoMars and Russian platform entry module.
Figure 8. Possible designs for Russian-designed lander.
Figure 9. Detail of one possible design for the Russian supplied lander.
Figure 10. Entry, descent, and landing plan for the ExoMars rover and Russian lander.
What makes the ExoMars 2018 project a dicey proposition is
the fact that the last Soviet/Russian rocket-powered landing occurred with the Luna
24 Moon landing in 1976. The Russians
have no recent experience with this type of machine. (Note that the Soviets soft-landed on Venus
as recently as 1985, but the lander deceleration was entirely through
atmospheric drag.) However, the upcoming mission of Luna 25, in 2016, is
set to fly a controlled soft-landing on the Moon. If successful, this may help ease any
concerns about Russian capabilities.
Mars' environment is different than that of the Moon, but the final
maneuvers leading to a soft-landing on these worlds is similar. Thus was the American lunar Surveyor
soft-lander a pathfinder for the later Viking spacecraft.
ESA has indicated that its 2016 EDM (Entry, Descent
and Landing Demonstrator Module) lander will play a role in
preparing for its following ExoMars effort.
To quote ESA's website, “ EDM will land on Mars to prove key
technologies for the 2018 mission.” This
is telling, and brings up the issue of how, exactly, the tasks required for
building this lander will be divided between ESA and Roscosmos. How much of the technology developed for
ESA's EDM mission will feed-forward to Russia's 2018 Mars lander? Will ESA share its software and/or hardware
developed for the EDM? In ESA's latest
Quarterly report, there is this quote, “ESA will provide the computer to manage
all operations except surface platform operations. The surface platform, being a Russian
responsibility, will be operated using a Russian-supplied computer. The Rover will also feature an ESA-provided
computer dedicated to Rover operations.”
Safely landing on Mars is perhaps the most difficult maneuver in the
field of planetary exploration and reliable software is an important
aspect. This division of computer labor could be a source of
concern.
ESA's EDM Mars
lander, referred to above, will use yet another landing technology. In lieu of airbags or landing legs or a sky
crane, it will utilize a crushable structure to attenuate the force of impact. (Figure 11) The
EDM will also use a set of 9 thrusters (3 clusters of 3 rocket engines
each). They will not be throttled as
were those on Surveyor, Viking, and the MSL Sky Crane. That capability is expensive to develop. Instead, the EDM will operate its thrusters
in pulse mode, the same method utilized by the Phoenix lander in 2008.
Figure 11. ESA's Entry, Descent and Landing Demonstrator Module (EDM)
This brings us to Phoenix-2, aka, Insight, NASA's
contribution to the international fleet of landers in 2016. It is now in Phase B, with construction set
to begin in 2014. However, every project has growing pains and one is revealed
through comments in NASA's newest budget proposal. Specifically, the document states, “If: Growth
of lander avionics and payload electronics continues to strain volume of
thermal enclosure, Then: The heritage design of the thermal enclosure and
aeroshell is at risk. The project cannot grow the size of the thermal
enclosure. Instrument teams are working
to close trade studies that will establish the baseline for payload electronics
configuration, and spacecraft team members are working closely with instrument
teams to identify and analyze overall configuration options.” One of the cost-saving aspects of Insight is
the use of the proven Phoenix lander design.
However, it appears that they are having difficulties in stuffing 11
pounds of instruments into a 10-lb bag, so to speak.
We will see four spacecraft utilizing four different landing
designs heading to the Red Planet in 2016 and 2018. It will be fascinating to see the results of
this fleet of ships.
