99942 APOPHIS · T−··· DAYS
FLY TO APOPHIS
A near-Earth flyby roughly once every 7,500 years · a deep-space mission led by Tsinghua University undergraduates
Shape from a lightcurve-inversion model (3D Asteroid Catalogue) · neck and surface details are artistic · Sq-type stony · non-principal-axis tumbling
99942 Apophis — named after the Egyptian god of chaos and destruction. At its discovery in 2004, it carried the highest “hazard rating” of any object in recorded history. The story is told in three steps.
Just after Christmas, the numbers from NASA's Sentry system kept climbing: the impact probability briefly reached2.7% (1 in 37). The Torino hazard index was pushed to —
A mean diameter of roughly 340–375 m — longer than three football fields laid end to end. Had it struck Earth, the energy released would have been about 100,000 times that of the Hiroshima bomb — fortunately, the impact risk was ruled out in 2021. This was not science fiction, but arithmetic the astronomers of the day had to face. On to the next step.
In March 2021, joint radar observations by Goldstone and Green Bank narrowed the orbital uncertainty to the kilometer level. JPL and then ESA removed Apophis from their risk lists — safe for the next 100+ years.
The threat is over. But a scientific opportunity that comes roughly once every 7,500 years has only just begun.
On April 13, 2029 at 21:46 UTC (05:46 Beijing time, April 14), Apophis sweeps past over the Atlantic, just 31,600 kilometers above Earth's surface — closer than geostationary satellites.
0km
Closest distance to Earth's surface · ~38,000 km from Earth's center
0km/s
Flyby speed · Apophis relative to Earth
2billion people
Visible to the naked eye · Europe / Africa / West Asia
0mag
Peak apparent magnitude · clearly visible under rural skies
Closest approach comes over the Atlantic; the visible zone covers the western half of the Eastern Hemisphere
Ground-based networks within China fall in the blind zone
So we send the telescope up
No years-long cruise into deep space — place the spacecraft in a 31,600-kilometer high orbit and lie in wait on Apophis's inevitable path. As mission chief scientist Bin Cheng puts it: "This is a 'doorstep' deep-space target."
01 · LAUNCH
Rideshare on a commercial rocket into a 1000 km / 55° low Earth orbit
02 · TRANSFER
378 days · 3,048 orbits · all-electric true trajectory (design values)
03 · STATION
Arrive early in the 31,600 km mission orbit and lie in wait for the target
04 · ENCOUNTER
7 km encounter · 8.74 km/s (relative to Apophis) · 8 cm/px
① HIGH-PRECISION GAZE
A two-axis gimbal locks onto a target streaking past at 8.74 km/s with ≤0.007° tracking accuracy (design value), holding motion blur below one pixel — like training a telephoto lens on a bird outside the window of a speeding bullet train, and keeping it sharp.
Gaze tracking accuracy (3σ)0.007°DESIGN ·Peak resolution8cm/px
See how sharp 8 cm/px really is →② WIDE-RANGE ELECTRIC TRANSFER
A 60 mN Hall-effect thruster — thrust equal to the weight of a sheet of A4 paper — drives the 200 kg spacecraft through 378 days, 3,048 orbits and 802 ignitions, climbing 30,000 kilometers up from low Earth orbit: the world's first all-electric transfer chain linking LEO to high orbit (true-trajectory design values). En route it crosses the Van Allen radiation belts again and again — auto-cutoff in eclipse, dose measured continuously orbit by orbit — surveying the danger zone into a 3D map along the way.
Hall thruster60mNDESIGN ·Delta-v4.11km/sDESIGN
DAY 000 · orbit 0
Inner belt (protons)Outer belt (electrons) · Repeated crossings · Auto-cutoff in eclipse · 3D radiation-belt survey →
③ PRECISION FLYBY
Acquire the target from 2 million kilometers out (design value) and autonomously guide down to a 7-kilometer closest approach — at a relative speed of 8.74 km/s, the entire golden window lasts only about 2 hours. There is no second chance.
Closest encounter range7km ·Golden observation window2h
Relative speed · spacecraft relative to Apophis
Student-led = undergraduates carry out mission design · spacecraft development · flight operations — 20+ undergraduates × 6 schools & departments
Commercially powered = commercial rideshare launch + commercial electric propulsion + socially raised funding — budget ≈ US$2.8M (university support + donations + sponsorships)
DESTINY+ scouts ahead, RAMSES rides alongside the whole way, OSIRIS-APEX orbits afterward — and START is the only one standing watch at closest approach. Complementary in time and space — not a race.
Advance flyby · Underway · 2028 shared launch with RAMSES
Flies past in early 2029, taking the first-ever close-range images of Apophis from space. Its primary mission is a 2030 flyby of Phaethon, parent body of the Geminid meteor shower — Apophis is a rehearsal en route.
Full escort · Underway · launching 2028-04 on H3
Arrives no later than 2029-03-01, on station before, during, and after the flyby. Fully approved at the November 2025 Ministerial Council, with a total investment of about €150 million.
Precision closest-approach flyby · In development · early-2028 commercial rideshare launch
On station at closest approach on 2029-04-14, capturing the golden 2 hours of tidal upheaval. The only mission staring from 7 km at closest approach — capturing the 2 hours when no one else is there.
Post-flyby orbit · In flight · Earth gravity assist completed 2025-09
Slips in about 1 hour after the flyby, then 18 months of close-up study. Extended OSIRIS-REx mission; will fire its thrusters to blow away surface material and observe the subsurface. Mission continues, with funding decided year by year.
✓ done● active○ planned◍ adjusting
20+ Tsinghua undergraduates form four task squads — science, mission design, spacecraft systems, and outreach — selected for Tsinghua's Disruptive Innovation Talent Program.
Five core members topped 128 teams from 53 universities — clearing 125 targets with the highest metric score nationwide.
Preliminary designs completed for the probe and the pathfinder satellite; first design review kicked off, with recruitment open across campus.
The first pathfinder satellite carries out in-orbit tests and astronomical observations to validate key technologies.
System design review completed; work moves into subsystem integration and prototype development.
Full-spacecraft assembly, integration, and test campaign completed, followed by the pre-shipment review.
Rides a commercial launch vehicle into a 1000 km / 55° low Earth orbit.
About 245 days and 1,730 orbits — the world's first all-electric transfer chain from LEO all the way to 31,600 km.
05:46 Beijing time (2029-04-13 21:46 UTC), a high-speed staring observation from 7 km.
T−··· DAYS
3-D radiation-belt survey · lunar-transfer validation · low-cost sampling technology demonstration.
Timeline reflects publicly stated plans · spaceflight schedules may shift · updated 2026-07
20+undergraduates
Students at every station of the mission
6schools & departments
Aerospace · Xingjian · Dushi · Astronomy · Zhili · Arts & Design
4task squads
Science · Mission Design · Spacecraft · Outreach
Faculty advisers: Li Junfeng · Baoyin Hexi · Wang Zhaokui · Wang Tianshu · Bin Cheng (Mission Chief Scientist)
