Apollo Entry

From Apollo mission reports here

Apollo 7 and 9 were earth orbit, slower reentry. Apollo 8 and 10 through 17 were lunar missions with high speed reentry of the command module. Apollo 11,12, and 14-17 were landing missions.

Useful graphs for Apollo 8, 10, and 11. I cannot find useful entry information after Apollo 11, so these three sets are hopefully representative of the other six lunar missions.

The command module had roll and attitude thrusters, which were used to indirectly control the trajectory. The center-of-mass of the command module was offset toward's the astronaut's feet. That edge of the CM would lead into the air stream; the capsule could be rotated with the roll thrusters so that the lift vector (directed towards the nose) vectored the spacecraft left, right, up, or down. The lift-to-drag ratio for the CM was approximately 0.3, so if the entry drag was near maximum at 6 gees, the lift vector would be about 2 gees, pointed whichever way was necessary to adjust the trajectory. Coming in above orbital velocity, the lift vector would be pointed earthward to keep the CM at the right altitude; below "Vcirc" the lift vector was pointed up to maintain altitude (and thus density and drag force).

The "entry scroll" is a paper graph that was preloaded into the Entry Monitoring System, and scrolled past a little window in the control panel between the left and center seats. If the computer failed, the command module pilot adjusted the roll and lift of the command module to follow the graph. There were two graphs, skip and no skip; if weather over the primary recovery site was bad, the computer (or the CMP manually) would select the "skip" graph and extend reentry by a few hundred kilometers. Apollo 11 skipped to avoid a storm, the other missions did not skip, and landed at the primary recovery site.

Except ... it looks like Apollo 16 DID do a skip, see below:

Click pictures for enlargements

Apollo 8

Entry Monitor System Scroll, Gees vs Velocity

attachment:a8a.png attachment:a8b.png

Roll vs Mission Elapsed Time

attachment:a8r.png

Apollo 10

Entry Monitor System Scroll, Gees vs velocity

attachment:a10ems.png

Roll and Altitude vs Ground Elapsed Time

attachment:a10roll.png attachment:a10alt.png

Gees and Lift/Drag vs Ground Elapsed Time

attachment:a10gee.png attachment:a10LD.png

Range and Vertical Velocity vs Ground Elapsed Time

attachment:a10range.png attachment:a10rdot.png

Apollo 11

Table III

EI time

Load g

V f/s

range n mi

° Bank

Rdot f/s

0:00

0.000

36190

1593

0:28

0.049

36276

1418

0:30

36277

0.0

-3186

1:18

-666

1:30

30176

54.43

211

1:56

1.057

22091

-86.68

Entry Monitor System Scroll, Gees vs Velocity

attachment:a11ems.png

Roll and Altitude vs Time from Entry Interface

attachment:a11roll.png attachment:a11alt.png

Gees vs Time from Entry Interface and Lift/Drag vs Mach Number (velocity)

attachment:a11gee.png attachment:a11LD.png

Range and Vertical Velocity vs Time from Entry Interface

attachment:a11range.png attachment:a11RDOT.png

Velocity vs Time from Entry Interface

attachment:a11vel.png

Apollo 12

Apollo 13 Mission report page 9-17, two brief paragraphs about entry and landing (useless)

Apollo 14 Mission report page 5-28, two brief paragraphs about entry and landing (useless)

Apollo 15 Mission report page 114, two brief paragraphs about entry and landing (useless)

Apollo 16 Mission report page 9-56, "entry deceleration exceeded 7 gees" (semi-useless)

Apollo 16 was the highest gee reentry.I wonder why??? According to the flight journal,

PAO = Public Affairs Officer:

Apollo 17 Mission report page 190, no trajectory data (useless)

Entry energy

Without the service module providing air, electricity, and cooling, the command module could not survive a big skip far above the atmosphere, though it did make a small skip to adjust the splashdown range (and Apollo 11 made a slightly larger skip to pass over a storm). The first skip lowered capsule velocity below Vcirc

So, the Apollo skip did not allow a higher speed Vinf, but a larger skip might be permitted for a Mars mission with hours of consumables onboard for the crew. That would allow a two pass entry trajectory with a first skip exit above Vcirc but significantly less than Vesc.

At 40 km altitude (6420 km radius equatorial), Vcirc = 7.88 km/s, so V²circ = 62.1 km²/s². For a LEO/MEO mission with a Vinf less than 8.7 km/s (such as AS-202 in the table below), V² is less than 76.0 km²/s², and less than 14 km²/s² of V² must be shed for a circular trajectory. On the other hand, for a lunar entry trajectory with a Vinf of up to 11.27 km/s, incoming V² can be as high as 127 km²/s², so 65 km²/s² must be shed during a lunar re-entry. For a flat trajectory, V² = 2 a d, so if d is limited then a acceleration must increase, as much as 4.6 times.

Apollo (and some Mars probe missions) use the drag and capsule L/D ≈ 0.3 to create negative (downward) lift, which curves the trajectory downwards and increases the path-length d. Otherwise, the shallow hyperbolic curve would only briefly touch the dense atmosphere long enough to provide significant acceleration.

As late as 1963, it was assumed that capsule L/D might range between 0.5 and 2.0, which would have significantly improved drag. Wind tunnel testing (at speeds far below Apollo entry) suggested an L/D of 0.37, while flight test showed an 18% reduction to 0.3 or less. The space shuttle had an L/D of only 1.0, very small compared to the Concorde ( L/D = 7 at Mach 2) or the Boeing 777 ( L/D = 19 ) or a thermal-soaring glider ( L/D = 70 ). Wider wings creating more lift would be torn off by reentry forces.

Ref: "The Dynamics and Flight Environment of Lifting Vehicles Entering the Atmospheres of Earth, Mars, and Venus", Phillip Levine (Avco, MA), pp. 349-375 in Dynamics of Manned Lifting Planetary Entry, Wiley, 1963

At 40 km altitude (6420 km radius equatorial), Vcirc = 7.88 km/s and V²circ = 62.1 km²/s² . Without the cm

NASA SP-4009 The Apollo Spacecraft - A Chronology

W=Wikipedia

P = NASA Post-launch Report

C =

Launch

Mission

rocket

perigee

apogee

entry

max

L/D

heat

error

km

km

km/s

gees

MW/m²

km

05/28/64

AS-101

Wx

S1

182

227

decay June 1, 1964

09/18/64

AS-102

Wx

S1

177

206

decay September 22, 1964

02/16/65

AS-103

Wx

S1

500

736

decay July 10, 1985

05/25/65

AS-104

WP

S1

511

739

decay July 8, 1989

07/30/65

AS-105

WP

S1

521

536

decay August 4, 1969

02/26/66

AS-201

WP

S1B

425

8300

72

07/05/66

AS-203

Wx

S1B

184

214

exploded in orbit

08/25/66

AS-202

WP

S1B

1143

8690

380

11/09/67

Apollo 4

WE

S5

204

18092

11139

7.3

16

Lift down 22 sec

01/22/68

Apollo 5

Wx

S1B

162

214

decay February 12. 1968

04/04/68

Apollo 6

Wx

S5

32

22225

10000

3rd stage partial fail

80

10/11/68

Apollo 7

WP

S1B

227

301

7911

3.33

3.5

12/21/68

Apollo 8

WP

S5

lunar

11065

6.84

0.300

297

2.6

03/03/69

Apollo 9

WP

S5

204

497

7921

3.35

5.0

05/18/69

Apollo 10

Wx

S5

lunar

11094

6.78

0.305

292

2.4

07/16/69

Apollo 11

Wx

S5

lunar

11032

6.56

0.300

301

3.1

11/14/69

Apollo 12

Wx

S5

lunar

11008

6.57

0.309

298

3.7

04/11/70

Apollo 13

Wx

S5

lunar

11037

5.56

0.291

292

1.9

01/31/71

Apollo 14

Wx

S5

lunar

11025

6.76

0.280

308

1.1

07/26/71

Apollo 15

Wx

S5

lunar

11267

6.23

0.290

294

1.9

04/16/72

Apollo 16

Wx

S5

lunar

11033

7.19

0.286

317

5.6

12/07/72

Apollo 17

Wx

S5

lunar

11000

6.49

0.290

317

1.9

ApolloEntry (last edited 2017-11-22 23:14:55 by KeithLofstrom)