spx-16 dragon unberth and release on gmt 2019-01-13 page

VEHICLE SpX-16 Dragon Unberth and Release on GMT 2019-01-13 PAGE 1/5

1. INTRODUCTION

The SpaceX-16 "Dragon" cargo ship was released from the International SpaceStation (ISS) on GMT 2019-01-13 at about 23:33. This was the first splashdownand recovery at night for the Dragon. The commercial cargo vehicle returned avariety of space research that will handed off to NASA engineers and distributedto investigators around the world.

SpaceX-16 Dragon completed a ~36-day mission attached to the station’s Node 2(Harmony) module after delivering several thousand pounds of science and supplieson GMT 2018-12-08. The departure of Dragon left four visiting vehicles, includingNorthrop Grumman’s Cygnus cargo ship, attached to the space station as depictedin Figure 1.

If all goes as planned, then the next Dragon mission to the space station will beSpaceX’s first vehicle capable of transporting crew to the ISS. However, this firstone will be an uncrewed demonstration mission, designated SpaceX DM-1, to verifyreadiness of ground systems, orbit-to-docking activities and landing operations.

2. QUALIFY

Figure 2 on page 2 is a color spectrogram computed from Space AccelerationMeasurement System (SAMS) sensor 121f05 measurements made in the JapaneseExperiment Module (JEM) during the unberth and release activities. The arrowannotation shows some of the vibratory impact related to those activities. AtGMT 22:45, attitude control was transitioned to US-only thruster (USTO) mode ofoperation resulting in a train of impulsive accelerations that tend to excite structuralmodes below about 2 Hz. These vibrations show up initially as vertical, yellowishstreaks on the spectrogram followed by brief orange/red horizontal streaks untilthe excitation (spectral peaks) settles down. Attitude is held leading up to Dragonrelease at ~GMT 23:31, then USTO pattern mentioned earlier is repeated startingat GMT 23:39.

3. QUANTIFY

The Microgravity Acceleraion Measurement System (MAMS) would have beenthe instrument to best measure the quasi-steady effects of the unberth/release 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 low-pass filtered SAMSdata in an attempt to quantify the vibratory impact.

SSA+X-axis is in flight direction+Z-axis is in nadir direction

+X

as of GMT 2018-12-08

+X

as of GMT 2019-01-13

+Z

The cropped image in the red rectangle at the left shows the location of the “Dragon-16” cargo ship before unberthing.

The larger image below shows the vacated nadir port of Node 2 after Dragon departure.

+Z

Fig. 1: Visiting vehicle arrangement before (top) & after (bottom) Dragon departure.

VIBRATORY MODIFIED JANUARY 17, 2019


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Start GMT o]−January−[No9m No]7o8:NN:NN

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GMT 22:45Transition to USTOprior to Dragon releaseat ~GMT 23:31

Fig. 2: Spectrogram during Dragon unberth/release activities on GMT 2019-01-13.

Figure 3 on page 3 shows acceleration Root-Mean-Square (RMS) values versustime. These RMS values (below 2 Hz) were computed from SAMS sensor 121f02measurements made in the JEM during the same span as the spectrogram of Figure2. As the 2 annotations on that page show, there were notably large impactsduring the 2 spans when USTO was used to control attitude before and afterDragon release. The unberth and release events do not show as impactful tothe transient/vibratory environment. Instead, the maneuvering and attitude controlrequired to orchestrate a clean and safe departure are where we focus for transientand vibratory impacts as shown in Figure 3 through Figure 5 for SAMS sensors inthe JEM, Columbus and US Lab modules, respectively.

RMS values below 2 Hz in the Columbus module topped out just under 250 µgduring USTO control as seen in Figure 4. On the other end of the RMS magnitude

scale, the smallest impact was in the US LAB at about 75 µg, see Figure 5.

4. CONCLUSION

The RMS results presented here reinforce the fact that SAMS sensors in the JEMand COL tend to experience higher magnitude structural mode excitation than thosein the US LAB due to the layout, structure and nature of the ISS. In the case ofa Dragon release as described in this document, the driving force and source ofexcitation were thrusters needed to change or maintain the space station’s attitude,primarily before and after the actual release event.

VIBRATORY MODIFIED JANUARY 17, 2019


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Start GMT 13−January−2719= 713p18:77:77

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SSAnalysis[ 7]7 7]7 7]7]

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�f: 7]779 Hz= Range: 7 − 2 Hz142]7777 sapsec .6]77 HzH

sams2= 121f72776 at JPM1A6= RMS Console= Seat Track:[377]92 −354]84 273]74]

GMT 22:45Transition to USTOBefore Dragon Release

GMT 23:39Transition to USTOAfter Dragon Release

Fig. 3: RMS below 2 Hz for Dragon release time frame with SAMS sensor (121f02) in JEM.VIBRATORY MODIFIED JANUARY 17, 2019


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SAMS2, 121f08006, COL1A3, EPM, near PK−4, 6.0 Hz (142.0 s/sec) Hanning, k = 1SSAnalysis[ 0.0 0.0 0.0]

.

Temp. Resolution: 57.690 sec∆f: 0.009 Hz, Range: 0 − 2 Hz142.0000 sa/sec (6.00 Hz)sams2, 121f08006 at COL1A3, EPM, near PK−4:[371.17 287.43 165.75]

Fig. 4: RMS below 2 Hz for Dragon release time frame with SAMS sensor (121f08) in COL.VIBRATORY MODIFIED JANUARY 17, 2019


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GMT 22:45Transition to USTOBefore Dragon Release

GMT 23:39Transition to USTOAfter Dragon Release

Fig. 5: RMS below 2 Hz for Dragon release time frame with SAMS sensor (121f03) in US LAB.VIBRATORY MODIFIED JANUARY 17, 2019

spx-16 dragon unberth and release on gmt 2019-01-13 page

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