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As was typical of the conclusion of Shuttle-era FRRs, a formal launch date is usually posted. However, the launch of SpaceX\u2019s cargo-laden Dragon capsule \u2013 atop a Falcon 9 booster from Cape Canaveral Air Force Station (CCAFS) Launch Complex-40 (LC-40) \u2013 is tracking April 30, but that is pending the resolution of a couple of open items that require additional testing relating to software on the ISS side.<\/p>\n
As of this time, April 30 is still the target for what will become a date of historical significance with the occurrence of the first ever launch of a privately-owned rocket and spacecraft to the ISS.<\/p>\n
Monday\u2019s FRR also carries some historical significance, as the first launch of a private spacecraft \u2013 widely touted as the \u201csuccessor\u201d to the Space Shuttle \u2013 has been approved on the very same day that the first Space Shuttle orbiter to head off into retirement spent her last full day at the Kennedy Space Center, with the responsibility for ISS support now reluctantly handed off from the seasoned Space Shuttle orbiters to their eager young commercial siblings.<\/p>\n
Dragon mission overview:<\/p>\n
The long-anticipated combined COTS-2\/COTS-3 (C2\/C3), also known as Demo-2\/Demo-3 (D2\/D3) and officially noted as the SpX-D mission, will be the first visit of SpaceX\u2019s Dragon spacecraft to the ISS, with major vehicle modifications over the only previous Dragon flight in December 2010 being rendezvous and berthing systems, and spacecraft trunk complete with solar arrays and radiators.<\/p>\n
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Following launch on April 30, Flight Day-1 (FD-1) and FD-2 will see Dragon perform the far field phasing portion of its mission, during which time checkouts of Dragon\u2019s Absolute GPS (AGPS), free drift and abort capabilities will be performed. FD-3 will see Dragon perform a 2.5km fly-under of the ISS to test Dragon\u2019s Ultra High Frequency (UHF) communication via the COTS UHF Communication Unit (CUCU) on ISS.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z314.jpg\" "\\"Z3\\"")
FD-3 will also see other tests being performed on Dragon, such as Dragon command ability by the ISS crew (strobe light switch on) via the Crew Command Panel (CCP) connected to the CUCU, and a Relative GPS (RGPS) checkout between Dragon and ISS. At the end of FD-3, the ISS Mission Management Team (IMMT) will meet with SpaceX managers to determine whether C2 mission objectives have been successfully satisfied.<\/p>\nShould C2 objectives be met, the IMMT will give a go-ahead for FD-4\u2019s attempt at C3 objectives, which include a full Dragon rendezvous with the ISS, flying to within 30m of the station in order to be grappled by the Space Station Remote Manipulator System (SSRMS) and berthed (not docked) to the Node 2 Nadir port by Expedition 31 astronauts Don Pettit of NASA and Andr\u00e9 Kuipers of ESA, working from the ISS\u2019 Cupola observation\/robotics station.<\/p>\n
Although free-flyer captures have been performed previously on ISS during the Japanese HTV-1 and HTV-2 missions, the Dragon capture may be slightly more challenging.<\/p>\n
\u201cThere\u2019s unknowns with these new vehicles [because] they haven\u2019t been there [ISS] before, and from the past experience we know HTV has been very very solid, which made it relatively easy to capture,\u201d explained NASA astronaut Joe Acaba \u2013 who will arrive at the ISS aboard Soyuz TMA-04M roughly two weeks after Dragon\u2019s arrival \u2013 to NASASpaceflight.com\u2019s Philip Sloss during a pre-flight interview.<\/p>\n
\u201d These others [commercial vehicles], they\u2019re a little bit lighter with some bigger thrusters, so there may be more motion that we might see, so they may be a little bit more challenging.\u201d<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z413.jpg\" "\\"Z4\\"")
Following the opening of the ISS Node 2 Nadir and Dragon Common Berthing Mechanism (CBM) hatches and mating of all power\/air hoses and ventilation between ISS and Dragon on FD-5, Dragon will enjoy a roughly two and a half week stay at the ISS, during which time Dragon\u2019s non-essential cargo will be transferred to the station and trash\/return items loaded in its place.<\/p>\nAfter the completion of the cargo transfers, Dragon will be unberthed from the ISS and released by the SSRMS for a re-entry and splashdown off the coast of California \u2013 thus regaining some marginal down-mass capability for the ISS Program that retired along with the Space Shuttles last year.<\/p>\n
(A more in-depth overview of the C2\/C3 mission will be covered in a separate article on NASASpaceflight.com.)<\/p>\n
ISS ready to receive Dragon:<\/p>\n
Dragon\u2019s destination, the ISS, is now fully ready to receive its first commercial guest, following a SpX-D Stage Operations Readiness Review (SORR) preformed on 5th April, the presentation for which, along with other SORR presentations and an impressive set of exclusive ISS on-orbit status notes and images, are available to view and download on L2 (L2 Link).<\/p>\n
With hardware and software transitions successfully completed earlier this year, and ISS robotic assets prepared last week for Dragon\u2019s arrival, only a few issues relevant to the Dragon mission were noted in the SORR presentations, all of them minor and classed as low risk, and with all bar one being cleared as having no impact to SpX-D flight operations.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z58.jpg\" "\\"Z5\\"")
The only issue listed as having a \u201cpotential\u201d issue to SpX-D flight ops was the recent 2A Beta Gimbal Assembly (BGA) pointing command issue and subsequent transaction errors. BGAs provide beta rotation capability to allow the Solar Array Wings (SAWs) to track the sun.<\/p>\n\u201cControllers saw a suppressed caution for an invalid BGA 2A Pointing Control Command. At the same time transaction errors were seen on the UB-PVA-24-1 bus and a channel swap from A to B. Data shows the transaction errors were due to no response from RTs (Relay Terminals) outboard of the BMRRM (Bearing Motor Roll Ring Module) which points to a potential issue with the signal ring in the BMRRM.\u201d<\/p>\n
The SORR presentation noted: \u201cTransaction errors are consistent with hypothetical short due to FOD (Foreign Object Debris) in the signal roll ring of the BMRMM. There is one spare BMRMM stowed on-orbit. EVA procedures to replace a faulty BMMRMM are mature\u201d.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z610.jpg\" "\\"Z6\\"")
Over the next few weeks, numerous similar transaction errors continued to occur on Channel B, causing swap overs to Channel A and subsequent swap backs to Channel B. From reviewing data, flight controllers were able to determine that: \u201cAll 5 of the most recent sets of transaction errors have now occurred between BGA angles of 27 degrees \u2013 30 degrees\u201d.<\/p>\nAfter remaining on Channel A for a few days in order to prevent further transaction errors on Channel B, a meeting of the Failure Investigation Team (FIT) determined that the forward plan, which is currently in effect, was to switch back to Channel B for 40 days to gather data on bus performance. \u201cThe automated response to swap bus channels in response to the loss of data connectivity will be inhibited to gather information on how long the data dropouts last\u201d, continued the notes.<\/p>\n
While the 2A BGA transaction errors was the only issue noted as having a potential impact on the SpX-D mission \u2013 although the issue is still classed as low risk and acceptable to flight, despite being ongoing \u2013 there were other notable issues that relate to the SpX-D mission that were cleared as being no impact.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z74.jpg\" "\\"Z7\\"")
The Cupola, the seven-windowed observation module from where the SSRMS will be controlled during Dragon\u2019s capture, offers increased situational awareness over simple video monitors inside the ISS. However, the means by which this is achieved \u2013 360 degree windows \u2013 have been having some minor issues of their own of late.<\/p>\n\u201cCupola Window 6 Temperature Divergence \u2013 Specialists have been tracking a divergence between the two temperature sensors on Cupola Window 6. This signature has been seen in the past on Window 5 when a laptop was placed near one of the temp sensors,\u201d stated L2 ISS on-orbit status notes. \u201cThe crew was asked about Cupola configuration, but there were no laptops or other heat generating equipment near Window 6\u201d.<\/p>\n
Using a temperature probe, the crew took readings near the window temperature sensors. Based on those readings, no noteworthy divergence between the windows was detected, however there was a noticeable difference between the temperature sensor reading and manual reading for Window 6 RTD (Resistance Temperature Device) 2.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z93.jpg\" "\\"Z9\\"")
\u201cDuring Passive Thermal Control System\u2019s team Cupola Window temperature scans they noticed that Cupola Window 6 exceeded its upper temperature limit of 100 degrees F (37.3 degrees C) at 38.3 deg C for 13 minutes,\u201d added the notes. \u201cPer Flight Rules, if any Cupola window exceeds 36.7 degrees C for more than 5 minutes, the shutter must be closed.<\/p>\n\u201cExceeding the upper limit is a concern for the Cupola window seal. Engineering is assessing the temperature violation and its duration. The window shutter has been requested to remain closed until this assessment is complete. Upper Cupola Window temperatures can be managed by closing the window shutters when not in use.\u201d<\/p>\n
Notes the following day mentioned that temperature exceedance issues had also occurred on Cupola Window 1: \u201cThe Cupola Window 1 (Port) temperature exceeded the 36.7\u00b0C watch limit and maxed out at 39.3\u00b0C. It was above the limit for approximately 7 minutes. The flight rule only allows for <5 minutes above the 36.7\u00b0C limit.\u201d<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z101.jpg\" "\\"Z10\\"")
\u201cPer the Flight Rules, the ground requested the crew to close the Window 1 shutter and the temperature began to drop. The concern is the integrity of the seals around the window. This small exceedance is not considered a hazard, but the elevated temperatures are under investigation for potential causes and prevention.\u201d<\/p>\nAs for probable causes, the SORR presentation noted: \u201cOn 25\/03\/12, window scratch panes (with heaters) were R&R for ATV-3 antenna photography. Leading theory is partial delamination of RTD 2 is possible; may have exacerbated during scratch pane removal (not easily accessible for inspection)\u201d.<\/p>\n
While the investigation into the window temperature issues is still ongoing, since the exceedance values are low and an adequate mitigation (closing the shutters) is available, this allowed the issue to be classed as being no risk to the SpX-D flight.<\/p>\n
Another minor issue was noted which related to the Space Integrated GPS\/Inertial Navigation System (SIGI), which will be utilised by Dragon during Relative GPS (RGPS) communication with the ISS. There are two SIGIs aboard the ISS, although one had been showing signs of ageing.<\/p>\n
\u201cSIGI-1 is near end of its 10 year life and an unused internal gyroscope has caused multiple failures recently. All were recovered by power cycles. The SpaceX LCC (Launch Commit Criteria) requires 2 SIGIs, after that only 1 is required for rendezvous and capture,\u201d stated the SORR presentation. <\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z111.jpg\" "\\"Z11\\"")
\u201cDragon will abort during rendezvous if data is not available from an active SIGI within 5 or 10 minutes (depending on proximity to ISS). Following a power cycle, an ISS SIGI takes a minimum of 30 minutes to recover functionality\u201d.<\/p>\n\u201cSpaceX and ON prefer to R&R (Remove & Replace) SIGI-1 to increase the likelihood of mission success. There are 2 spares on orbit and 4 on the ground. R&R requires ~7 hours crew time, requires repeat of the 12 channel checkout, and 3 weeks run time prior to LCC. ON recommended R&R of SIGI-1 to minimize the likelihood that degraded internal gyroscope will cause it to fail during Dragon rendezvous.\u201d<\/p>\n
As continued by L2 ISS on-orbit status notes: \u201cOn April 4, the SIGI-1 was R&Rd. It was placed in first priority for both ISS State and Attitude on April 6. Yesterday, ground controllers completed the final checkout for SpaceX operations \u2013 a 12 channel test. The data dump for the 12-channel test is still under evaluation, however the test was nominal\u201d.<\/p>\n
As such, the SIGI issue is now considered resolved and is classed as no impact to the SpX-D mission.<\/p>\n
![\"\"](\"https:\/\/www.nasaspaceflight.com\/wp-content\/uploads\/2012\/04\/Z12.jpg\" "\\"Z12\\"")
Only one other minor issue pertains to the SpX-D mission, which is a slightly open protective petal on the Node 2 Nadir (N2N) Active Common Berthing Mechanism (ACBM) port to which Dragon will attach. In addition to internally removable Center Disk Covers (CDCs), ACBM petals provide protection for the ACBM \u2013 specifically the berthing ring \u2013 that would otherwise be exposed to space.<\/p>\nThe four petals (one for each quadrant of the berthing ring) on each vacuum-exposed ACBM on the ISS are designed to open and close (like a flower petal \u2013 hence their name) remotely when commanded in order to expose the berthing ring. If a petal were to become stuck open, it would leave the ACBM berthing ring open to MMOD (Micro Meteoroid Orbital Debris) strikes, and if a petal were to become stuck closed, it would preclude a berthing from occurring.<\/p>\n
As stated by the SORR presentation: \u201cDuring an SSRMS pre-motion survey, the N2N ACBM Petal #1 (Starboard-Aft) appeared to be slightly open, although mostly closed. This condition was not noticed during a recent N2N CBM survey and checkout, due to the camera angles used at that time\u201d.<\/p>\n
\u201cPer photo review, the petal #1 position may have been in this configuration since STS-123\/Flight 1J\/A (March 2008), when the Petal #1 launch restraints were released. Petal #1 is not believed to be warped and both sides appear to be the same displacement above adjacent petal covers. Petal #1 has been through approximately 15 successful open\/close cycles with no issues.\u201d<\/p>\n
\u201cStatus: A prep for mate (exercising the latches and opening the petals) will be performed approximately 40 hours prior to berthing. After the SpaceX Dragon demo is berthed, OSO (Operations Support Officer) will ask if the crew could inspect Latch #1 to see if it is different from the others.\u201d<\/p>\n
Thus, with all ISS issues determined to be low risk and of little or no impact to the SpX-D flight, the SORR concluded that: \u201cThe ISS MER (Mission Evaluation Room) is Go for SpX Capture, Attached Ops, SpX Release and Stage operations\u201d.<\/p>\n
(Images: L2\u2019s SpaceX Dragon C2\/C3 Mission Special Section \u2013 Containing presentations, videos, images, interactive high level updates and more, with additional images via NASA and SpaceX). <\/p>\n
(Click here: http:\/\/www.nasaspaceflight.com\/l2\/ \u2013 to view how you can access the best space flight content on the entire internet).<\/p>\n","protected":false},"excerpt":{"rendered":"
For the first time in history, NASA\u2019s extensive Flight Readiness Review (FRR) process has concluded that a privately-owned spacecraft is tentatively cleared to visit the International Space Station (ISS). With a launch date still tracking April 30, the SpaceX Dragon spacecraft will lift off toward a space station that is now fully prepared to extend a […]<\/p>\n","protected":false},"author":1,"featured_media":30414,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[9091,2304,1395,479,3610,233,316],"class_list":["post-40153","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-news","tag-cots","tag-crs","tag-dragon","tag-falcon-9","tag-frr","tag-iss","tag-spacex"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/40153"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=40153"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/40153\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media\/30414"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=40153"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=40153"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=40153"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}