Multi-Mission Radioisotope Thermoelectric Generator Heat Exchangers for the Mars Science Laboratory Rover
- Tuesday, 03 January 2012
These heat exchangers can be used in any application in which heat loads must be simultaneously collected and rejected from opposite sides of the same structure.
The addition of the Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) to the Mars Science Laboratory (MSL) Rover requires an advanced thermal control system that is able to both recover and reject the waste heat from the MMRTG as needed in order to maintain the onboard electronics at benign temperatures despite the extreme and widely varying environmental conditions experienced both on the way to Mars and on the Martian surface (See figure).
MSL Rover in Stowed Cruise Configuration showing HXs positioned on both sides of finned MMRTG." class="caption" align="right">Based on the previously successful
Mars landed mission thermal control
schemes, a mechanically pumped fluid
loop (MPFL) architecture was selected
as the most robust and efficient means
for meeting the MSL thermal requirements.
The MSL heat recovery and
rejection system (HRS) is comprised of
two Freon (CFC-11) MPFLs that interact
closely with one another to provide
comprehensive thermal management
throughout all mission phases. The first
loop, called the Rover HRS (RHRS),
consists of a set of pumps, thermal control
valves, and heat exchangers (HXs)
that enables the transport of heat from
the MMRTG to the rover electronics
during cold conditions or from the
electronics straight to the environment
for immediate heat rejection during
warm conditions. The second loop,
called the Cruise HRS (CHRS), is thermally
coupled to the RHRS during the
cruise to Mars, and provides a means
for dissipating the waste heat more
directly from the MMRTG as well as
from both the cruise stage and rover
avionics by promoting circulation to
the cruise stage radiators.
A multifunctional structure was developed that is capable of both collecting waste heat from the MMRTG and rejecting the waste heat to the surrounding environment. It consists of a pair of honeycomb core sandwich panels with HRS tubes bonded to both sides. Two similar HX assemblies were designed to surround the MMRTG on the aft end of the rover. Heat acquisition is accomplished on the interior (MMRTG facing) surface of each HX while heat rejection is accomplished on the exterior surface of each HX. Since these two surfaces need to be at very different temperatures in order for the fluid loops to perform efficiently, they need to be thermally isolated from one another. The HXs were therefore designed for high in-plane thermal conductivity and extremely low throughthickness thermal conductivity by using aluminum facesheets and aerogel as insulation inside a composite honeycomb core. Complex assemblies of hand-welded and uniquely bent aluminum tubes are bonded onto each side of the HX panels, and are specifically designed to be easily mated and demated to the rest of the RHRS in order to ease the integration effort.