NASA has postponed the next Dragon resupply mission to the International Space Station (ISS) after the release of station Main Bus Switching Units (MBSUs) – US ISS component of the orbital segment (PSB) Power System (EPS) – was seen this week. CRS-17 launch was slipped in at least two days while the issue is evaluated.
CRS-17 Dragon mission was set to start at the beginning of May 1, starting at the Falcon 9 rocket from SLC-40 pad at Cape Canaveral.
Booster spacecraft and are in the last stage of preparation, the carrier rocket, the last successful by static fire and rollback to interface with the spacecraft Dragon. Starting Readiness Review (LRR) and 'End of Loading »were the only unresolved issues in the flow direction of the launch.
Nevertheless, NASA canceled the launch of the following issues with the electrical system at the station, which had the potential to affect the safe grip of the dragon, as soon as it came later in the week.
In fact MBSUs electrical junction boxes for the orbital outpost. Two channels have gone done, which means loss of redundancy for some key hardware associated with the arrival of the dragon.
MBSU have been problems before, with the channels 2A and 2B suffered a problem in 2017. Replacement work was carried out using SSRMS.
US station power is generated by using eight station solar arrays Wings (surfactant) at 160 volts DC (VDC), which is known as the primary energy. From each of the eight sawmills, main power switches to the appropriate Direct Current Switching Unit (DCSU).
A complete overview is given in the PSB EPS 182-page EPS ISS training manual, available for download from the ISS section on L2.
At a time when drinking in the sunlight (ie, power generation), the DCSUs send some power directly to one of the four MBSUs, and some force to the respective charge / discharge of the battery group (BCDU), which in their turn will charge the saw batteries for use during periods of orbital darkness.
During orbital darkness when the saw does not create power, DCSUs send battery power directly to one of four across the MBSA tool transfer assembly (ATO), which facilitates the transfer of energy through the Solar Alpha rotating joint (SARJ). There are two UTAS ISS – one for SARJ port and one to starboard SARJ.
After power passed into UTA, four MBSUs ISS each received power DCSUs powered by two, and four such MBSUs therebetween distribute power from all eight DCSUs and related surfactants them. These DCSU supply channels known as channels, and designated as 1A, 1B, 2A, 2B, 3A, 3B and 4A, 4B – is the same as their corresponding surfactant (i.e. surfactant 1A 1A channel channels).
Deficiency observed in the ISS refers to two of these channels specific to MBSA 3.
"The main bus switching (MDS) 3 Loss of communication – a critical loss occurred on the bus MBSU 3, battered load on 3A and 3B channels," said L2 ISS status information.
"The main effects include Ku-band, the Alpha Magnetic Spectrometer (AMS), CMG-3 and the Space Station Remote Manipulator System (SSRMS) redundancy. "
The last of the & # 39 is the key to the arrival of the dragon. While one channel is available for use SSRMS NASA likes redundancy available in the case of delivery during capture.
Troubleshooting is not easy. In MBSUs distribute power from each of its two input channels DCSU for DC to DC conversion units (DDCUs) via Remote Bus isolators (calves). DDCUs in turn, convert 160 VDC power primary current (which may occasionally vary approximately plus or minus 10 volts, depending on the output of surfactants) in a steady 124 V DC, known as secondary power.
With DDCUs, secondary power 124 V DC is sent to the busbars PSB, where it passes through the remote power control module (RPCM) circuit breakers, where he finally can be obtained with the help of user loads.
Some MBSUs also send the main force of the American Russian conversion units (Arcus), which transform the 160 V dc Peninsula primary power supply in a standard 28 VDC Russian segment (RS) power, which, in turn, distributed on the Russian modules in addition to the Russian Solar Energy array (completed task for US EVA-18 involved in routing the power cables from the MBSA to CSF, for use in the direct future module). MBSUs may also be cross-linked if needed to effectively migrate SAE architecture PSB.
From a physical point of view, all four box MBSUs installed on the S0 Truss, as they were to start S0 TRUSS over ten years ago, on STS-110 in April 2002, although MBSUs were designed to be EVA replaced as part of a module of the ISS philosophy of design ".
NASA conducted Failure Investigation Teams (FIT), to work through the problem.
"Troubleshooting, was not successful and the team evaluate the possibility of power failure. The attack is planned, "added information L2 ISS. "The team is working on a console based on the cross-connect plans and alternative supply chain to maintain the basic load.
As of Monday, KU-band message was changed again and the AMC channel load to 4A and restored nominal operation.
Other issues at the plant have also been noted around this event, using the remote power control module (RPCM) S01A_B remote power controller (RPC) 2 Trip, apparently in connection with the question of MBSA.
"In response to the denial MBS 3 and operating power loss to the control point gyroscope (CMG) -3, team tried to close RPCM Z14B_B RPC 12 so as to provide power for heater survival CMG 3. When attempting to closing, the RPC load open" added information L2 ISS.
"This type V external RPCM and susceptible to a hybrid field effect transistor (FET) issues. Teams working in the heat and hours discussing plans for mitigation. "
This article will be updated when additional information is available.