spx-17 dragon capture and install gmt 2019-05-06 page

VEHICLE SpX-17 Dragon Capture and Install GMT 2019-05-06 PAGE 1/5

1. INTRODUCTION

For the SpX-17 resupply mission, the Dragon spacecraft’s pressurized capsulewas loaded with 1,517 kilograms (3,344 lb) of equipment and supplies, while afurther 965 kilograms (2,128 lb) of unpressurized cargo was stored in the trunksection, for a total of 2,482 kilograms (5,472 lb).

The pressurized cargo includes 726 kilograms (1,601 lb) of scientific equipmentand experiments. Research equipment that SpX-17 delivered to the station includesTissue Chips in Space, Photobioreactor, the Hermes Facility and equipment neededto augment the Space Acceleration Measurement System (SAMS). This includes:

• 2 sensor heads• 2 seat track devices• 4 cable assemblies• 8 wireless adapters• 2 USB drives

Along with experiment equipment, the SpX-17 mission delivered 338 kilograms(745 pounds) of supplies and provisions for the space station’s crew, 357 kilograms(787 lb) of hardware for the US and International segments of the station, 75kilograms (165 lb) of computer equipment, 10 kilograms (22 lb) of hardware tosupport EVAs and 11 kilograms (24 lb) of hardware that is being flown on behalfof the Russian Federal Space Agency.

After the Dragon’s cargo was unloaded, the capsule would be filled withequipment to be returned to Earth. Because its capsule is designed to be recovered,Dragon provides NASA and their international partners with the ability to returnfailed hardware to Earth for investigation, experiments for further analysis, andequipment to be refurbished and reflown.

Dragon’s unpressurized Trunk contains hardware that will be mounted on theoutside of the space station. This includes the Orbiting Carbon Observatory 3(OCO-3) payload, which will use three spectrometers to measure the density anddistribution of carbon dioxide in Earth’s atmosphere.

SpaceX-17 Dragon is scheduled to be docked to the ISS for about one monthbefore its departure and return to Earth. Figure 1 shows a depiction of the visitingvehicle arrangement after the SpX-17 Dragon was berthed to the nadir-facing portof the Node 2 module.

Nominal Attitude(SSA)+X-axis is in flight direction+Z-axis is in nadir direction

+X

+Z

Fig. 1: Visiting vehicle arrangement with Dragon berthed at Node 2 (nadir).

2. QUALIFY

Figure 2 on page 2 is a color spectrogram computed from Space AccelerationMeasurement System (SAMS) sensor 121f03 measurements made in the US LABbefore, during and after the capture and install activities. The white text annotationsshow some of the pertinent activities that impact the vibratory environment. Mostnotably, at GMT 09:24, attitude control was transitioned to US-only thruster(USTO) mode of operation resulting in a series of thruster firings intended toadjust or maintain the space station’s attitude during the rendezvous.

Thruster firings, being impulsive accelerations, tend to excite structural modesbelow about 2 Hz. These vibrations show up initially as vertical, yellowish streakson the spectrogram followed by brief orange/red horizontal streaks until theexcitation settles down. Attitude is held leading up to Dragon capture at ~GMT11:00, then USTO pattern mentioned earlier is resumes starting at GMT 11:07 andthen dies down around GMT 12:46 with transition to momentum management forattitude control.

VIBRATORY MODIFIED MAY 14, 2019


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08:50-08:57 Maneuver to Dragon Capture Attitude09:24 Transition to USTO10:56 Attitude Hold11:00 Dragon Capture11:07 Transition to USTO11:43-11:53 Maneuver to Dragon Berthed TEA12:46 Transition to Momentum Mgmt using USTO12:55 Disable Thrusters for Dragon Install13:35 Enable Thrusters After Install


Fig. 2: Spectrogram during Dragon capture/install activities on GMT 2019-05-06.

3. QUANTIFY

The Microgravity Acceleraion Measurement System (MAMS) would have beenthe instrument to best measure the quasi-steady effects of the capture/install ofDragon and the shift of overall ISS center of mass. However, the MAMS was outof service during these events, so here we take a look at RMS acceleration below2 Hz to quantify the vibratory impact.

Figure 3 on page 3 shows acceleration Root-Mean-Square (RMS) values versustime. These RMS values (below 2 Hz) were computed from SAMS sensor 121f03measurements made in the US LAB during the same span as the spectrogram ofFigure 2. As the annotations on this plot show, there were notably large RMSimpacts during the period when USTO was used to control attitude before and

after Dragon capture/install. The capture and install events themselves do not showup as impactful to the transient/vibratory environment. Instead, the maneuveringand attitude control required to orchestrate a clean and safe rendezvous are wherewe focus for transient and vibratory impacts as shown in Figure 3 through Figure5 for SAMS sensors in the US Lab and Columbus modules.

RMS values below 2 Hz in the Columbus module topped out just over 500 µgduring USTO control as seen in Figure 5. On the other hand, the RMS magnitudesin the US Lab came in at a bit under 200 µg. This disparity comes about due tothe structural mode response at the Columbus measurement location relative to theUS Lab measurement location. In Columbus, we see larger accelerations stemmingfrom larger displacements.

4. CONCLUSION

The RMS results presented here reinforce the fact that SAMS sensor theColumbus tend to experience higher magnitude structural mode excitation thanthose in the US LAB due to the layout, structure and nature of the ISS. In thecase of a Dragon capture/install as described in this document, the driving forceand source of excitation were thrusters (USTO) needed to change or maintain thespace station’s attitude, primarily before and after the actual Dragon capture/installevents.

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DragonInstall

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Fig. 3: RMS below 2 Hz for Dragon capture time frame with SAMS sensor (121f03) in JEM.VIBRATORY MODIFIED MAY 14, 2019


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Fig. 4: RMS below 2 Hz for Dragon capture time frame with SAMS sensor (121f04) in US LAB.VIBRATORY MODIFIED MAY 14, 2019


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Fig. 5: RMS below 2 Hz for Dragon capture time frame with SAMS sensor (121f08) in COL.VIBRATORY MODIFIED MAY 14, 2019

spx-17 dragon capture and install gmt 2019-05-06 page

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