NASA JPL Space Simulators

NASA/JPL-Caltech. Public domain (NASA / US government work).

NASA JPL’s environmental test organization operates two thermal vacuum chambers used by planetary surface programs: the 25-Foot Space Simulator in Building 150, a 1961 chamber with off-axis xenon solar simulation, and the smaller 10-Foot Vertical Space Simulator, whose floor rides a hydraulic lift so that a tightly packed test configuration stays accessible [1][2]. Both hold Mars pressure and Mars temperature on flight hardware that cannot drive; the driving is done outdoors at the MarsYard, which holds neither.

These are environmental test facilities rather than robotics laboratories, and the 25-Foot chamber is a NASA-owned facility available to other government agencies and to private industry [1][2].

Laboratory data

Parameter	Value
Operator	NASA JPL environmental test organization [1]
Location	Pasadena, California, United States
Commissioned	25-Foot Space Simulator, 1961; 10-Foot chamber date not published
Type	Thermal vacuum chambers, one with off-axis solar simulation [1][2]
Floor area	Not published. The 25-Foot chamber stands 25.9 m tall in Building 150
Capabilities	25-Foot and 10-Foot Vertical Space Simulators
Simulant or terrain	No simulant bed. Geoanalogue rocks placed on keyed baseplates [2]
Instrumentation	600 thermocouple channels and 40 RTD channels to the article [1]
Ground truth	Kendall cavity radiometer on the solar beam; six ion gauges
Fidelity limits	Chamber conditions are hard to vary between tests and are held fixed [2]
Access	Available to other government agencies and to private industry [1]
Cited by	Curiosity [3], Phoenix arm [4]

Capabilities

25-Foot Space Simulator

Parameter	Value
Working volume	6.1 m diameter x 7.6 m high with the solar simulator; about 21.3 m high without
Test article limits	Wall hard points rated 10,000 lb each; door 4.6 x 7.6 m
Vacuum	5 x 10^-5 torr in about 3 hours, into the 1 x 10^-6 torr range on cryopumps
Temperature	-185 C on liquid nitrogen; -125 to +100 C on gaseous nitrogen
Illumination	2.0 to 11.0 solar constants, beam 8.5 to 18.5 ft, 37 xenon arc lamps
Slope	Not applicable
Gravity offload	Not applicable. Articles are hard mounted or suspended at 1 g
Instrumentation	600 thermocouple, 40 RTD and 60 heater control channels to the article

Source: [1].

The chamber is 25.9 m high and 8.2 m in diameter, and its useful test volume depends on the mode: 6.1 m diameter by 7.6 m high with the solar simulator running, or about 21.3 m of height without it [1]. Access is at ground level through a 4.6 by 7.6 m door, and articles enter on a monorail crane from the high bay. Structural support is either hard mounting to stanchions that pass through the floor shroud onto columns bearing on an isolated seismic mass below the end bell, or suspension from wall-mounted hard points rated to 10,000 lb each [1].

Pumping runs in four stages and reaches 5 x 10^-5 torr in about three hours, with the cryopumps and turbopumps taking it into the 1 x 10^-6 torr range [1]. The shroud system sets the thermal boundary: louvered aluminum panels, black on every surface facing the test volume, at -185 C on liquid nitrogen or anywhere from -125 C to +100 C on temperature controlled gaseous nitrogen. Mars surface conditions are produced as a gas fill rather than as vacuum: approximately 8 torr of nitrogen for the MSL rover system thermal test [3].

Solar simulation is off-axis. Thirty-seven xenon arc lamps feed an integrating lens unit that mixes their output into a uniform beam, which passes a fused quartz window and reflects from a 23 ft collimating mirror at the top of the chamber [1]. Swapping between two integrating lens units and two collimating mirrors gives four beam diameter and intensity combinations spanning 8.5 to 18.5 ft and 2.0 to 11.0 solar constants. The best-characterized combination, the 18.5 ft beam at 2.0 solar constants, has a collimation half angle of 1.1 degrees with 96.2 percent of energy inside 1 degree and uniformity of +0.6 to -1.4 percent; the 8.5 ft beam at 11.0 solar constants is looser, at a 2 degree half angle and plus or minus 5 percent [1].

10-Foot Vertical Space Simulator

Parameter	Value
Vacuum	Approximately 7 torr for Mars surface work; base pressure not published
Temperature	Nominal cold testing at -65 C, with stress cases to -115 C
Illumination	No solar simulator
Simulant or terrain	Geoanalogue rocks on keyed standard baseplates at fixed positions

Source: [2].

The distinguishing feature of the smaller chamber is its layout. The floor, the end bell, rides a hydraulic lift: lowered, it sits at first-floor level and the entire test configuration is accessible; raised, it mates to the shrouds at second-floor level and the chamber seals. That arrangement gives full access to a tightly packed test configuration in a small footprint, which is why it was chosen for the Mars 2020 sampling and caching campaign [2].

Instrumentation

The 25-Foot Space Simulator’s data system provides 600 thermocouple channels of type E or T and 40 RTD channels to the test article, with 60 heater control supplies of 75 W each [1]. Facility instrumentation is separate: 140 thermocouple channels on the shrouds, mirror and structure, six ion gauges, a Kendall cavity radiometer measuring the solar beam, and three temperature-controlled quartz crystal microbalances watching contamination [1].

For arm and drill work in the smaller chamber the instrumentation is indirect. Target rocks are scanned into a 3D point cloud and loaded into the Rover Sequencing and Visualization Program Hyperdrive simulator, and arm and drilling operations are always validated in simulation before execution to prevent hardware damage [2].

What it does not reproduce

Gravity. Neither chamber offloads. Articles are hard mounted, suspended or stood on the floor at Earth weight [1][2].

Driving. Neither chamber has a terrain bed a vehicle can traverse. Mobility work goes to the MarsYard, which cannot hold Mars pressure or temperature.

Chamber conditions as a per-test variable. In the Mars 2020 sampling campaign, rock and hardware configurations were fixed for a given chamber pumpdown, and chamber conditions were difficult to vary from test to test, so temperature and pressure for a given configuration were generally held unchanged. The test plan was built around that constraint as a design of experiments rather than against it [2].

Camera geometry. The limited space in the vacuum chamber meant flight-like cameras could not be positioned where they sit on the physical rover, so the campaign built its 3D environment model from a fixed CAD model of the static chamber plus rock samples on keyed standard baseplates at predetermined locations and orientations, instead of from rover imagery [2].

Solar flux and Mars pressure and a moving tool, together. The 25-Foot Space Simulator has xenon solar simulation and has run Mars surface conditions as an 8 torr nitrogen fill [1][3]; the 10-Foot chamber has run approximately 7 torr and -65 C with real rock targets but no solar simulator [2]. The Phoenix icy-soil delivery failure needed all of it at once. Insolation on ice-bearing regolith held in the aluminum scoop warmed the sample enough that it adhered to the scoop wall and would not fall through the TEGA inlet on the first two attempts; a third sample obtained by scraping, with less ice, did not congeal and was delivered [4]. Reproducing that on the ground requires Mars pressure, Mars-relevant sample temperature and a representative solar flux on the tool at the same time, sustained through a transfer sequence of realistic duration. The Phoenix Payload Interoperability Testbed, at the University of Arizona, reproduced the delivery geometry closely enough that overlaid Robotic Arm Camera images from Mars and from the testbed were used to correct scoop positioning over an instrument inlet [4], but not that thermal combination.

Campaigns run there

MSL rover system thermal test, 25-Foot Space Simulator, 2011. The 900 kg Curiosity rover was run for 16 days in simulated cruise conditions under vacuum and in simulated Mars surface conditions under 8 torr nitrogen, at mission-extreme hot and cold boundaries [3]. A xenon lamp solar simulator imposed solar loads during a bounding hot case and a simulated Mars diurnal case. All thermal hardware performed nominally and the Rover Heat Rejection System, the liquid loop that moves heat in and out of the chassis electronics boxes, performed better than predicted. Steady state and transient data were used to correlate the thermal models that then predicted Gale Crater performance, with critical hardware predicted to stay within allowable limits across the 669 sol surface mission [3].

Mars 2020 sampling and caching qualification, 10-Foot Space Simulator, 2019 to 2021. A two year series at approximately 7 torr and -70 C, with cold testing nominally at -65 C and stress cases to -115 C, on a chamber floor filled with geoanalogue rocks including deliberately selected challenge rocks [2]. Hardware was phased in as fidelity became available, ending with a qualification model adaptive caching assembly, corer, gas dust removal tool and facility contact sensor, and an engineering model robotic arm. Totals across the series: 6 qualification coring bits took 66 cores, 1 abrading bit made 34 abrasion patches, 1 regolith bit collected regolith twice, and 17 seals were activated [2]. Sample tubes and seals were reused after cleaning, unlike flight. Flight software itself was deployed into the test environment rather than a test-specific build, which was new for the project [2].