HTV-2 Resupply Craft launches towards Space Station

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Representing the third spaceflight of 2011, JAXA’s HTV-2 vehicle, atop the H-IIB rocket, launched at 1537 JST (0137 CST) from the Tanegashima Space Center in southern Japan. With its second flight, the HTV will deliver thousands of pounds of internal and external cargo to the International Space Station (ISS) and serve as a means for equipment disposal from the Station upon the craft’s undocking and destruction in the atmosphere.

Launch/On-Orbit Comm & Radar Tracking Ops:

The H-IIB launch vehicle is a two-stage rocket using liquid oxygen and liquid hydrogen as propellant and has four strap-on solid rocket boosters (SRB-A) powered by Polybutadiene.

The H-IIB has two liquid rocket engines (LE-7A) in the first-stage, instead of one for the H-IIA. It has four SRB-As attached to the body, while the standard version of H-IIA had two SRB-As. In addition, the H-IIB’s first-stage body has expanded to 5.2m in diameter from 4m of H-IIA.

The vehicle is extended by the total length of the first stage by 1m from that of H-IIA. At the result of such enhancement, the H-IIB requires 1.7 times more propellant than the former.

To support the launch and initial on-orbit phases of HTV-2’s flight, several ground-based radar tracking stations will be available to ground controllers in Japan.

In fact, HTV-2 will have four C-band radar passes during its first 6 orbits: one during launch and post-insertion activities, one from Kwajalein atoll during orbit 1 ops, one from Wallops field in Virginia, USA on orbit 5 ops, and a final ground pass from Wallops during the craft’s sixth orbit.

As the JSC (Johnson Space Center) MOD (Mission Operations Directorate) presentation to the HTV-2 FRR states, “Four (4) C-band radar passes will be available to support the HTV-2. In the event of a contingency, all available C-band radars would be brought up for support.”

Additionally, ground controllers will have near-permanent comm contact with HTV-2 from launch to docking, and then again from undocking -1 hr until reentry – a capability made possible via continuous S-band Single Access coverage and augmented by Multiple Access (MA) Forward/Return and S-band Multiple Access data channels.

Continuous S-band Single Access support will be routed, at times, through the TDRS (Tracking & Data Relay Satellite) system (TDRS-4, TD171, and TDZ) from pre-launch until ISS grapple and berthing. Likewise, MA service will be available through TDRS-4, TDW, and TDZ.

Nonetheless, TDRS-4’s battery #1 is failed and, while there were no battery issues during the last “eclipse” from 24 July 2010 – 25 September 2010, the next “eclipse” period runs from 21 January 2011 – 23 March 2011… nearly the entire duration of HTV-2’s mission. As the JSC MOD presentation (available for download on L2) notes, “TDRS-4 downlink experiencing irregular, apparently random telemetry errors (hits).”

This could result in telemetry errors from HTV-2. A backup system, Spare Traveling Wave Tube Amplifier (TWTA) is available for use should this issue be realized in flight.

Likewise, “Full utilization on the Eastern and Western TDRS satellites” will be available to HTV-2 teams, but the TDRS 275 satellite will be available for SSA only through its SA2 antenna.

The SA1 antenna will not be available for use except during docking and undocking only and even then must be limited and preapproved by the NASA Network Director.

TDRS support will not be required during HTV/ISS docked ops.

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Flight Dynamics/Automated Vehicles/Orbit Analysis:

After its insertion into LEO (Low Earth Orbit), HTV-2 will begin a seven (7) day phasing period where its orbit will be gradually adjusted (at the same time the spacecraft itself is put through a series of post-launch/pre-docking tests) to more precisely align the craft with the International Space Station.

Unique to HTV-2 is its relatively wide margin in terms of rendezvous altitudes, with a capability to rendezvous with the ISS at altitudes between 350 and 460 km. As noted by the Flight Dynamics, Automated Vehicles & Orbit Analysis presentation to the HTV-2 FRR, “The 350 km minimum altitude is the actual ISS altitude (i.e. ISS perigee requirement) and not average altitude.”

A unique consideration for HTV-2’s docking, however, quickly became the need to set up both HTV-2 and Shuttle Discovery rendezvous opportunities in late-January/early-February following the delay of STS-133/ULF5 to a penciled in “work to” date of 3 February.

“ISS trajectory will be optimized to meet requirements for STS-133/ULF5 and HTV-2,” notes the FRR presentation – available for download on L2. Since APM (Ascent Performance Margin) for STS-133 became a driving factor for the rendezvous altitude of Discovery’s mission, the ISS team devised a plan to lower the Station’s orbit to 348 km (188nm) to assist with STS-133’s APM needs.

This initial strategy allowed for the set-up of FD-3 (Flight Day 3) rendezvous capability for Discovery for the week-long early-February launch window while still preserving HTV-2 launch and docking ops in late-January.

To this end, ISS reboost maneuvers were planned for December 22 and January 12. “TIG for the ISS reboosts on December 22 and January 12 will be optimized to minimize the eccentricity and keep the ISS perigee as high as possible” for HTV-2.

HTV-2/Discovery SIMO Ops:

Moreover, the shift in NASA’s launch schedule for Discovery led to direct impacts on HTV-2 mission planning. With Discovery’s launch suddenly falling within the time span of HTV-2’s docked mission – an occurrence which at first was not possible due to HTV-2’s berthing location and the payload needs of Discovery’s 133/ULF5 mission – a plan was devised to allow both vehicles to be docked simultaneously.

Under the initial planned outlined in the December 2010 FRR for HTV-2, HTV-2 would launch on January 20 and be grappled and berthed to ISS Node-2 Nadir via the SSRMS (Space Station Remote Manipulator System) on January 27.

The following day, the External Platform on HTV would be removed and installed onto the JEM EF (Japan Experiment Module Exposed Facility). On January 30, HTV power would then be deactivated and the HTV-2 itself relocated to the Node-2 Zenith port.

The following day, on January 31, the Russian Progress 41P spacecraft would dock to the Russian segment of the station and therefore pave the way for the STS-133/Discovery launch on 3 February.

However, as noted by the Mission Operations Directorate presentation to the HTV-2 FRR, the power and data cables needed to ingress HTV after its relocation to Node-2 Zenith had already been packed and stowed inside the PMM (Permanent Multipurpose Module) in Shuttle Discovery’s payload and would therefore not be aboard Station prior to FD-7 of Discovery’s mission – the day the PMM would be ingressed.

Therefore, a “Plan to provide temporary keep-alive power using old JLP cable, and comm via Prox RF; also building back-up power cable” was devised by ground teams to enable the relocation of HTV and its ingress by the crew prior to the arrival of Discovery and the PMM.

While the dates for this relocation operation have now changed given the alterations to Discovery’s launch date, they will still be performed prior to Discovery’s now-schedule NET (No Earlier Than) launch on 24 February.

With Discovery launching in February, HTV-2 will still be able to serve as the disposal vehicle for 2 RSP racks, 2 ISP (Integrated Stowage Platforms), and several large foam blocks from the PMM that will no longer be needed once the equipment they are carrying to orbit is removed.

In fact, 55-percent of HTV-2’s return trash content is scheduled to be from the PMM hauled to orbit by Discovery. To accomplish this, the ISS crew will devote nearly 210 hrs to the reconfiguration of the PMM to pull out all the equipment scheduled for burn up in Earth’s atmosphere on HTV-2.

Some of the trash, specifically the foam material from the PMM, will be stowed in “non-standard return stowage locations (center volumes, end-cone, PBA/PFE volumes).”

Resolution of HTV-1 In-Flight Anomalies:

Finally, as with all space missions, JAXA thoroughly reviewed all IFAs (In Flight Anomalies) from the HTV-1 mission in 2009 and developed workarounds or fixes to those issues. In all, only four IFAs gained mention in the HTV-2 FRR, the first being a loss of telemetry during HK1 preemption or packet swap.

As noted by the FRR, “SSIPC lost telemetry during HK1 preemption or packet swap. SSIPC ground system requires BIU minor frame counter in order to process telemetry.”

The presentation goes on to explain that this parameter (BIU minor frame counter in order to process telemetry) is only present – in HTV-1 – in HK1 packets 2 and 4, not in packets 1 and 3. Therefore, an HK1 swap between packets 1 and 3 “would mean SSIPC could not see Ess data. HK1 preemption while in 2 or 4 meant SSIPC could only see half of HTV telemetry.”

The necessary telemetry has been placed in all HK1 packets for HTV-2; however, preemption is still classified as an issue and “will be solved by avoiding preemption during critical HTV ops (handled in planning process).”

Further action on this topic will result in HTV-3 and subs having the BIU counter telemetry in the Ess packet so that preemption will not affect data in the SSIPC.

The second IFA identified from HTV-1 related to a MCU loss of sync caution annunciation.

“During activation of HTV-1, C&W (caution and warning) event 16415 ‘Primary INT MDM (multiplexer/Demultiplexer) Detected Loss of Sync with HTV MCU 2 – LAB’ was Enabled per step 8.4 in 1.100 HTV Activation (HTV OPS/HTV1). This event was in alarm, which rang tones onboard.”

Investigation into this issue revealed that an alarm during HTV activation was unavoidable for HTV-1 due to the default settings of the INT MDM – a setting that “would have been discovered preflight if HTV 1553 connection was modeled in SSTF.”

For HTV-2, “Event 16415 will remain inhibited during HTV attached ops unless a swap to MCU2 is required for a failure. In that case, event 16415 will be enabled and the loss of comm message for MCU1 (event 16414) will be inhibited,” notes the FRR presentation.

Finally, the last two IFAs both dealt with the GPS system aboard HTV-1.  As noted by the FRR, the HTV-1 GPS Absolute Kalman filter diverged once every 18 to 24hrs. This has been corrected for HTV-2 via a fix to the clock management module that “had a software bug causing the SIGI Kalman filter to periodically reject measurements and the filter to diverge.”

Moreover, the HTV-1’s GPS receiver experienced spontaneous resets every few days. To correct this issue, HTV-2’s GPS receiver firmware has been modified.

(Images via JAXA and L2 HTV presentations – over 50 FRR, FOR and Overview presentations).

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