Coming home: reentry

Duk wani dan sama yana zuwa gida a kan hanya daya: ta hanyar juya gudu zuwa zafi. A capsule zuwa daga orbit ke da isasshen makamashi ga kilogaram na ya tafasa kansa nauyi a cikin ƙarfe sau da yawa a kan. Dukkan sana’ar sake shiga ita ce ta warware wannan ƙarfin da sauri don ya tsira, kuma da sauri ba zai sake dawowa cikin sararin samaniya ba.

Jirgin ya fara tashi. Hasken rana yana yin taƙaitarwa.

Look

1. The deorbit burn. Pointing backwards, the capsule fires its engine for a few minutes and slows down by about 100 m/s. Kuma lalle ne, haƙĩƙa, Allah Ya saukar da shi a cikin sammai.
2. Entry interface, about 120 km up. The capsule meets the first thin traces of air still moving at about 7.8 km/s.
3. Fireball. An rufe iska a gaba da rufin zafi sosai har ta zama plasma mai haske, da digiri dubu masu zafi. Ƙarawa zuwa ga jerin gwano Kuma lalle ne, haskensa yanã tafiya a cikin duhu.
4. The corridor. Da za a dawo daga wata da 11 km/s, gefen shiga ya kamata ya zama daidai zuwa wani ɓangare na digiri: mai tsayi sosai kuma rage gudu zai shafe tawagar, mai ƙarancin yawa kuma capsule ɗin zai yi ta skim daga sama kamar duwatsu masu fita daga ruwa.
5. Parachutes. A ƙasan kilomita 10, kwayoyin suna faɗuwa a cikin mintuna kaɗan na kilomita / h. Parachutes bude, kuma ya sauka a mita kaɗan a kowane minti.

Understand

Daga cikin wani 400 km circular orbit (r = 6,778 km) da sauri ne 7.67 km / s. Wani ellipse wanda mafi karancinsa shine 50 km sama yana da a = 6,603 km, kuma a 400 km gudun sa ya kamata ya zama 7.57 km/s. The deorbit burn shi ne bambanci: game da 102 m/s, kawai 1.3% na orbital gudu.

An yi amfani da shi a cikin Ƙungiyoyin A da B. Air density ρ roughly halves every 5 km of descent (scale height about 7.2 km), so the deceleration rises steeply, peaks, and falls as the capsule slows. A cikin hoton sama:

Entry	Speed	Angle	Peak deceleration
Dakata	7.85 km/s	1.5°	game da 8 g
Da watã idan (haskensa) ya cika.	11 km/s	8°	game da 31 g
Daga watan, a cikin kofa	11 km/s	5.6°	game da 7 g
Da watã idan (haskensa) ya fãɗi.	11 km/s	4.8°	skips back out

Real capsules fly with a little lift (their center of mass is off-center, so they fly tilted) and roll to steer it, which lowers the peak to about 4 g for a Soyuz and widened Apollo’s corridor to about 2 degrees.

Master

Wannan siffar tana hada ma’aunin motsi na planar da na gravity da kuma drag kawai:

dv/dt = −μ r/|r|³ − (ρ(h) |v| / 2β) v,   ρ(h) = ρ₀ e^(−h/H)

da β = m/(C_D A) = 350 kg/m² (kabi na kwayoyin halitta) da H = 7.2 km. Don shiga balistiki mai tsayi, Allen da Eggers (1958) sun nuna cewa matsakaicin raguwa yana kusa da ya zama maras dangantaka da β:

a_max ≈ v_E² sin γ / (2 e H)

A cikin yanayin da ya fi tsayi (γ = 8°) yana ba da kimanin 44 g; simulation mai cikakke yana ba da 31 g, saboda matsin lamba yana ci gaba da juya hanyar ƙasa kamar yadda capsule ke sauka. A kowace hanya, da shiga gefen, ba girman jirgin sama, saita g-load, wanda shi ne dalilin da ya sa duk mai dawowa spacecraft flys wani m corridor.