Good question. As a physicist, I'll provide some general insights, though I don't have the exact details. Perhaps someone can offer more information from official sources or news articles. Based on my knowledge, here are some key points:Why is the suitable window of opportunity so far out (March)? If this were a manned mission or to supply a space station, wouldn't it be appropriate to get the docking done as fast as possible?
To add/clarify/summarize the above ...(Hope this helps)
ISRO's SPADEX satellite docking experiment, initially planned for January, may be delayed until March due to orbital constraints. The experiment involves docking two satellites, SPADEX-1 and SPADEX-2, in a low Earth orbit (LEO). However, the current orbital positions of the satellites are not favorable for docking, and ISRO is waiting for a suitable window to perform the experiment. (Technically delay no big deal)
SpaceX has been sending cargo ships to dock with the International Space Station and make it seem routine. The Russians too have been docking their cargo ships with the ISS for quite a few years. Is it easier to get the docking done because there are humans in the ISS who can help with the maneuvering of the cargo ship?
Comparison with ISS Docking Missions:
- SpaceX and Roscosmos have developed mature systems for ISS resupply, making these operations routine. The ISS maintains a stable orbit (relatively speaking), and docking procedures have been fine-tuned over decades. Automated docking systems, are robust and can operate autonomously, though crew presence on the ISS adds a layer of safety and contingency.
Human Presence is also a factor - While human assistance isn't strictly necessary for docking, having astronauts on the ISS allows for manual override and visual monitoring.
ISS resupply missions are operational, supporting a crewed station with a fixed schedule. SPADEX, by contrast, is a research and development mission,. This flexibility allows ISRO to prioritize mission success over speed. Not to mention energy cost (fuel -economy) is BIG priority.
Orbital Mechanics/ Constraints IMHO:
Windows: Docking two satellites in low Earth orbit (LEO) requires precise alignment of their orbits -- matching their altitude, inclination, and phase. (Unlike a space station like the ISS, which maintains a stable and predictable orbit, experimental satellites like SPADEX-1 and SPADEX-2 may have more limited orbital adjustments due to fuel constraints or operational design.) Finding a window might take weeks or even months. (No big deal) (see previous post by Ashokk - about fuel and solar panels)
- Delta-V Requirements: Complex maneuvers to synchronize the velocities of the two satellites, requiring small but precise adjustments (delta-V). Not *at all unusual* for ISRO to wait for natural orbital dynamics to reduce the energy (fuel) cost of these maneuvers..
Orbital Precession: Orbits in LEO are influenced by Earth's equatorial bulge, causing them to precess over time.
Demonstration vs. Operational Mission: Unlike manned missions or cargo resupply to the ISS, which have stringent timelines due to human needs or station operations, SPADEX is a technology demonstration. There is no immediate urgency, so ISRO can afford to wait for the optimal conditions to maximize the chances of success.
Keep in mind - SPADEX involves autonomous docking, a relatively new capability for ISRO. Extensive pre-mission testing, simulations, and software validation may be also be tested/validated/perfected.
Not to forget - ground-based support, such as tracking, telemetry, and command facilities, is also being validated. (See above post - 10-15 minutes window in each orbit )
Statistics: Posted by Amber G. — 15 Jan 2025 23:12