The Design and Engineering of Curiosity
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The Vehicle System Testbed’s avionics are similar to those of the flight rover, but are housed on a rack outside the rover’s body and connected to the rover’s body with an umbilical to facilitate testing. There is no RTG, so the same umbilical carries power. The umbilical is long enough to stretch the entire length of the Mars Yard. Like the flight rover, there are two complete main computer systems. While there is a cooling system, it is different from the one used on Mars. Because it’s on Earth, there is flexibility to reconfigure the VSTB as needed to accommodate tests. For example, prior to landing, the arm was removed and operated separately on a tiltable stand to allow engineers to do driving and arm testing simultaneously.
The VSTB has a full complement of engineering cameras, but does not have many flight-like science instruments. There is a flight-like MAHLI, which took the self-portrait in Figure 4.25. The APXS instrument is similar to the flight one but does not usually have its radioactive source (though the APXS team did once install a source for testing). Substitutes take the place of the ChemCam imager and Mastcams. There is no MARDI or CheMin. SAM electronics are present, but not the rest of the instrument. However, there are functioning SAM and CheMin inlet covers, and the engineers can collect sample material dropped through them in order to measure volume.
4.7.3 Scarecrow
Scarecrow is a second engineering model of the rover. It consists of a full-scale mobility system connected to a small body containing batteries and electronics. The whole model has a mass of 340 kilograms, or 3/8th of the mass of the flight rover, so that it exerts the same ground pressure on Earth that Curiosity does on Mars. Its name derives from the character in The Wizard of Oz: Scarecrow doesn’t have a brain. It does have force and torque sensors in its axles to measure wheel loading under Mars gravity. It can report motor current as well as roll, pitch, and yaw using onboard inertial measurement unit, much as the actual rover can. It has ultrasonic range finders on each wheel to measure sinkage.46 It is used primarily to test how well the rover traverses different types of terrain (Figure 4.26).
Figure 4.26. Scarecrow descending a slope in the Mars Yard, October 2007. NASA/JPL-Caltech image release PIA10014.
4.7.4 The Qualification Model Dirty Testbed
Before and shortly after landing, the tricky operations of drilling and sample preparation were worked out in the Qualification Model Dirty Testbed (QMDT). This had a non-flight-like arm with a high-fidelity duplicate of drill and sampling system. It was operated in a thermal vacuum chamber to mimic the Mars environment.
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Footnotes
1The description of Curiosity’s MMRTG in this section is based on NASA (2013), Jones et al (2013), and Woerner et al (2012)
2NASA Science Mission Directorate (2006)
3Woerner et al (2013), Woerner et al (2012)
4Gross and Cardell (2011)
5Welch et al (2013)
6Woerner (2014)
7JPL (2013a)
8JPL (2013b)
9David Woerner, personal communication, email dated June 16, 2016
10Lee and Donaldson (2013)
11Makovsky et al (2009)
12JPL (2014)
13Magdy Bareh, personal communication, August 28, 2017
14Davis (2012)
15Danny Lam explained the upgrades to me in an email on April 4, 2017
16Lee and Donaldson (2013)
17Keith Novak, personal communication, email dated February 28, 2017
18The description of the heat rejection system in this section is based on Novak et al (2013)
19Keith Novak, personal communication, email dated February 28, 2017
20Novak et al (2013)
21Cucullu et al (2014)
22Curiosity’s telecommunications hardware is described in Makovsky et al (2009)
23Ashwin Vasavada interview, February 6, 2014
24Edwards et al (2013a and 2013b) describe orbiter relay support for Curiosity
25Lakdawalla (2016)
26Ashwin Vasavada, personal communication, email dated January 11, 2017
27Ashwin Vasavada, personal communication, email dated January 11, 2017
28Bagla (2017)
29Lakdawalla (2015)
30Voosen (2016)
31Edwards et al (2013a)
32Sol 18 Mission Manager’s report, MSL Curiosity Analyst’s Notebook
33Sol 17 Mission Manager’s report, MSL Curiosity Analyst’s Notebook
34Edwards et al (2013a)
35There is no publication by an engineer that describes the rocker-bogie suspension system in detail. Sources for description of the mobility system include Heverly (2012) and Arvidson et al (2017)
36Matt Heverly, personal communication, email dated March 11, 2017
37Haggart and Waydo (2008)
38The investigation of causes of wheel damage is described in Arvidson et al (2017)
39Lakdawalla (2014)
40Steve Lee, personal communication, review dated August 13, 2017
41Herkenhoff (2017)
42James Erickson, personal communication, interview dated September 18, 2014
43JPL (2008)
44A sign in the Mars Yard shed states that MAGGIE stands for “Mars Automated Giant Gizmo for Integrated Engineering,” but that is likely a backronym for the name, the original source of which is lost to history
45Vandi Verma, personal communication, email dated February 9, 2017
46Heverly et al (2013)
© Springer International Publishing AG, part of Springer Nature 2018
Emily LakdawallaThe Design and Engineering of CuriositySpringer Praxis Bookshttps://doi.org/10.1007/978-3-319-68146-7_5
5. SA/SPaH: Sample Acquisition, Processing, and Handling
Emily Lakdawalla1
(1)The Planetary Society, Pasadena, CA, USA
5.1 INTRODUCTION
Curiosity has unprecedented capability for interacting with the Martian surface using a collection of hardware called the Sample Acquisition, Processing, and Handling (SA/SPaH, pronounced “saw-spaw”) system (Figure 5.1). SA/SPaH includes the robotic arm and turret, the drill, and the sample scooping/sieving/portioning apparatus called Collection and Handling for In situ Martian Rock Analysis (CHIMRA, pronounced “chimera”). Also included in SA/SPaH are the Dust Removal Tool (DRT, but usually just called the “brush”), a variety of immobile hardware bolted to the front of the rover that supports sampling and drilling activities called the “sample playground,” and motorized inlet covers and spring-loaded wind guards for the SAM and CheMin instruments.
Figure 5.1. Parts of Curiosity’s Sample Acquisition, Processing, and Handling (SA/SPaH) system. Top image is the John Klein self-portrait from sol 177 (NASA/JPL-Caltech/MSSS); bottom image was taken during testing at Kennedy Space Center on August 13, 2011 (NASA release KSC-2011-6470), annotated by Emily Lakdawalla.
5.2 ROBOTIC ARM AND TURRET
Curiosity’s arm is huge. It measures 2.2 meters long from its base to the center of the turret. The arm weighs 101 kilograms; the turret alone is 34 of that.1 Curiosity’s arm has five degrees of freedom, provided by individual motors. The motors power five joints, in order of their position along the arm: the shoulder azimuth joint; shoulder elevation joint; elbow joint; wrist joint; and turret joint. The operation of most of these joints mostly mimics the flexibility of a human arm, except that Curiosity’s elbow is fully double-jointed. Curiosity’s arm was designed to be strong enough that an Earth copy, under Earth gravity, could support its own weight without any additional help, which makes testing motions using the testbed rover substantially easier than it might otherwise be.
5.2.1 Arm mounts
The arm exerts significant loads on the rover whether it is extended or stowed. While stowed, caging mechanisms restrain the arm’s motion. On the top of the shoulder bracket are three mechanisms that securely hold the turret when the rover is driving (and held it during launch and landing). A forward-projecting (“+X”) parapet captures the turret, and then the turret rotates 50°, pushing two hooks on the turret into two “duckbill” clamps on the bracket, whose flaring mouths guide the hooks into place. See Figure 5.1 for the locations of all these components.
Although the turret is tightly restrained to the rover’s left shoulder when stowed, the arm’s elbow joint only rests passively on its tripod-shaped bracket on the rover’s right side. The elbow has to be able to slide back and forth along the bracket because the front panel of the rover is made of aluminum and the arm’s tubular structure is titanium. Aluminum’s coefficient of thermal expansion is almost three times higher than that of titanium, so the front panel expands and contracts by millimeters more than the arm does over the 180°C range of temperatures that Curiosity experiences over the Martian seasons. The aluminum shoulder bracket that supports the arm incorporates flexures that allow the bracket to accommodate the differing thermal expansion of the bracket and the titanium shoulder motor.
5.2.2 Cabling
Running all the signals needed to monitor and control the arm’s motors and instruments to the rover’s computer was a major challenge. There are 920 different signals being monitored on the robotic arm, of which 555 are at the very end of the arm on the turret, including 300 within CHIMRA. The signals travel to the avionics through 10 meters of flex cable, 63 millimeters wide and 5 millimeters thick, strapped to the outside of the rover arm. To allow freedom of motion, the flex cable wraps several times around each of the five actuators in large spools. The flex cable from the arm debouches into a rover bulkhead on the rover’s left shoulder, where its signals transfer to a huge bundle of Kapton-wrapped round wires.
5.2.3 Turret
The turret is about 60 centimeters in diameter. The centerpiece of the turret is the drill. Attached to it are CHIMRA, the dust removal tool (brush), MAHLI, and APXS (Figure 5.2). The science instruments are separated from the drill by vibration isolator mounts to mitigate the effects of vibration from CHIMRA and drill percussion.
Figure 5.2. Parts of Curiosity’s robotic arm turret, including the drill, dust removal tool or brush (DRT), Collection and Handling for In situ Martian Rock Analysis (CHIMRA), and two science instruments, the MAHLI camera and APXS elemental analyzer. Navcam image NLA_400335692EDR_F0040000NCAM00107M
, taken during the first turret checkout on sol 32. NASA/JPL-Caltech/Emily Lakdawalla.