Free tools Windows power users keep installed
One-click scans. No signup required.
iTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
Spacecraft slow down near an asteroid to reduce their speed relative to it—not to stop moving through space. For a rendezvous, the spacecraft must arrive moving at nearly the asteroid’s speed and in the same direction. Otherwise, it will pass by too quickly to remain nearby for operations such as mapping or sample collection.
What “slowing down” means in space
An asteroid and a spacecraft are both moving around the Sun. The spacecraft may still be traveling rapidly in its orbit even after it has reduced its speed relative to the asteroid. The key measurement is the difference between their velocity vectors: both their speeds and their directions.
NASA’s Trajectory Browser describes the delta-v for a small-body rendezvous in terms of that vector difference. The spacecraft must change its trajectory so the difference is small enough to reach and remain near the target.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
Why not just fly straight to the asteroid?
A direct-looking path does not guarantee a rendezvous. If the spacecraft reaches the asteroid while moving much faster than it, it can cross the target’s vicinity and continue onward. That may be appropriate for a flyby, whose goal is to observe a body during a brief encounter, but not for a mission that needs to operate near it over time.
#1 Best Overall
A rendezvous therefore involves planning the encounter timing and the spacecraft’s trajectory around the Sun so it reaches the asteroid with a manageable target-relative velocity. NASA’s small-body trajectory material describes interception and velocity reduction as part of reaching orbit or operating near a target.
How OSIRIS-REx reduced its speed relative to Bennu
NASA reported that OSIRIS-REx carried out four approach maneuvers between August 17 and November 27, 2018. They reduced the spacecraft’s velocity relative to Bennu from about 1,100 mph (491 m/s) to 0.10 mph (0.04 m/s). The final-approach images were taken from about 40 miles (65 km) away. These are Bennu-relative speeds, not speeds relative to Earth or the Sun. NASA’s final-approach account describes the sequence.
NASA’s individual maneuver reports give rounded intermediate values:
Quick wins for a faster PC:
Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →- AAM-1: Designed to reduce Bennu-relative speed from about 1,100 mph (491 m/s) to 313 mph (140 m/s). NASA’s AAM-1 report.
- AAM-2: Designed to reduce it from 315 mph (141 m/s) to 11.8 mph (5.2 m/s). NASA’s AAM-2 report.
- AAM-3: Reduced it from approximately 11.7 mph (5.2 m/s) to 0.24 mph (0.11 m/s) in two burns. NASA said the burns were split because of constraints on pointing science instruments too close to the Sun. NASA’s AAM-3 report.
The figures come from separate reports and are rounded, so they should not be read as a perfectly continuous speed record. NASA also noted that the approach maneuvers shaped the trajectory for arrival and the start of proximity operations. NASA’s arrival account.
Why make several maneuvers instead of one big braking burn?
Approaching an asteroid is a navigation and control problem as well as a speed-reduction problem. The spacecraft must reach the intended position and viewing geometry, use observations to refine its navigation, and retain the ability to make controlled corrections as it gets closer.
A NASA technical report on OSIRIS-REx describes two large early burns followed by maneuvers using progressively lower-thrust systems. Finer control was needed below 200 km, and navigation had to stay within a corridor of range and solar phase angles that supported observations. NASA’s proximity-operations report.
Rank #4
The sequence is mission-specific. Bennu’s approach is an example, not a template that every asteroid mission follows.
Rendezvous is not landing
Matching the asteroid’s motion lets a spacecraft remain near it or begin orbital and proximity operations. It does not mean the spacecraft has landed. Surface contact or sample collection is a separate operation that comes after arrival; OSIRIS-REx first arrived at Bennu and then began proximity operations.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
