UNCONTROLLED RE-ENTRIES OF MASSIVE SPACE OBJECTS

4th International Space Debris Re-entry Workshop ESA/ESOC, Darmstadt, Germany, 28 February – 1 March 2018

• Uncontrolled re-entries of massive space objects during the last decade

• The uncontrolled re-entry of the Zenit second stage 2017-086D

• Status and decay time evolution of the Chinese space station Tiangong-1

Outline

Premise Space hardware re-entries can be of two types

CONTROLLED if the time of re-entry is controlled and the impact of debris is confined to a designated zone UNCONTROLLED if the time of re-entry and ground zone of impact are not controlled To characterize in a synthetic way the relevance of uncontrolled re-entries, a re-entry magnitude

ΜR was defined at ISTI-CNR as follows

ΜR =  log10 [(dry mass of re-entering object in kg) / 100] + 0.3

Dry Mass M0 of the re-entering object [kg]

Re-entry magnitude MR

M0 ≤ 50 MR < 0

50 < M0 ≤ 500 0 ≤ MR < 1 500 < M0 ≤ 5000 1 ≤ MR < 2

5000 < M0 ≤ 50 000 2 ≤ MR < 3 50 000 < M0 ≤ 500 000 3 ≤ MR < 4

500 000 < M0 ≤ 5 000 000 4 ≤ MR < 5

Sources of data Orbit of re-entered objects: US Space-Track Organization (www.space-track.org) Mass of re-entered objects: ESA’s DISCOS Database (discosweb.esoc.esa.int); Gunter’s Space Page (space.skyrocket.de); Spaceflight101 (spaceflight101.com)

ISTI-CNR uncontrolled re-entry magnitude scale definition

Relevance of uncontrolled re-entries [2008 – 2017] Large (RCS > 1 m²) catalogued intact objects re-entered into the Earth’s atmosphere during the last decade [2008 – 2017] 366 rocket bodies (mass between ∼50 kg and ∼9 300 kg, 42 with mass < 500 kg) 82 spacecraft (mass between ∼57 kg and ∼13 525 kg – launch mass including propellants, 14 with mass < 500 kg)

Ec ∼ 10−3

2 ≤ MR < 3 16 (4%) objects Ec ∼ 10−4

1 ≤ MR < 2 376 (84%) objects

Ec < 10−4

0 ≤ MR < 1 55 (12%) objects

 MR < 0 1 object MR 

M0

[kg]  Space Object

2.268 9300 SL-16 (2011-065B) 2.268 9300 SL-23 (2011-001C) 2.268 9300 SL-23 (2011-037D) 2.268 9300 SL-23 (2015-074C) 2.078 6100 DRAGON/FALCON9 (2010-026A) 2.078 6000 CZ-7 (2016-042E) 2.072 6000 CZ-7 (2017-021B) 2.085 5916 PROGRESS-M 27M (2015-024A) 2.053 5668 UARS (1991-063B) 2.041 5502 CZ-2F (2008-047B) 2.041 5502 CZ-2F (2011-053B) 2.041 5502 CZ-2F (2011-063B) 2.041 5502 CZ-2F (2012-032B) 2.04 5500 CZ-2F (2013-029B) 2.04 5500 CZ-2F (2016-057B) 2.04 5500 CZ-2F (2016-061B)

Dry mass M0 of the re-entering object [kg]

Re-entry magnitude MR

All intact objects

Spacecraft Rocket bodies

M0 ≤ 50 MR < 0 1 0 1

50 < M0 ≤ 500 0 ≤ MR < 1 55 (12%) 14 (17%) 41 (11%)

500 < M0 ≤ 5000 1 ≤ MR < 2 376 (84%) 66 (80.5%) 310 (85%)

5000 < M0 ≤ 9300 2 ≤ MR < 3 16 (4%) 2 (2.5%) 14 (4%)

All re-entered intact objects 448 82 366

Re-entry frequency [2008-2017] Large catalogued intact objects with mass > 500 kg re-entered into the Earth’s atmosphere between 2008 and 2017

324 rocket bodies (∼88% of large re-entered rocket bodies) 68 spacecraft (∼83% of large re-entered spacecraft)

30 32 24

36 34 33 39

34 34 28

4 4 4 8 6

12 9 7 6 8

34 36 28

44 40

45 48 41 40

36

0

10

20

30

40

50

60

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Num

ber o

f re-

ente

red

obje

cts

with

mas

s > 5

00 k

g

R/B SC R/B+SC Mass > 500 kg

Observed solar flux F10.7 between January 2008 and January 2018

Average re-entries per year

32 rocket bodies 7 spacecraft 39 intact objects

∼1 intact object every 1-2 weeks

Re-entry frequency [2008-2017] Large catalogued intact objects with mass ≥ 3900 kg re-entered into the Earth’s atmosphere between 2008 and 2017

40 rocket bodies (∼11% of large re-entered rocket bodies) 4 spacecraft (∼5% of large re-entered spacecraft – For Phobos-Grunt the propellant mass is included)

1 1 1 1 1

5

1 1

4

1 1 1

6

2 1 1

4

1

0

2

4

6

8

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Num

ber o

f re-

ente

red

obje

cts

with

mas

s >

5000

kg

SC R/B R/B+SC

Mass > 5000 kg

Mass ≥ 3900 kg

Space object

INTLDES

Re-entry epoch

Mass [kg]

Inc [deg]

CZ-2F R/B 2008-047B 17/10/2008 5502 42.39 DRAGON/FALCON 9 2010-026A 27/06/2010 6100 34.48 SL-23 R/B 2011-001C 19/03/2011 9300 51.39 SL-23 R/B 2011-037D 08/08/2011 9300 51.38 UARS 1991-063B 24/09/2011 5668 60.35 CZ-2F R/B* 2011-053B 10/10/2011 5500 42.78 CZ-2F R/B 2011-063B 08/11/2011 5502 42.77 SL-16 R/B 2011-065B 22/11/2011 9300 51.42 PHOBOS-GRUNT 2011-065A 15/01/2012 13525 61.73 CZ-2F R/B 2012-032B 26/01/2012 5502 42.77 CZ-2F R/B 2013-029B 21/06/2013 5502 42.77 PROGRESS-M 27M 2015-024A 08/05/2015 7289 64.76 SL-23 R/B 2015-074C 02/01/2016 9300 51.36 CZ-7 R/B 2016-042E 28/07/2016 6000 40.79 CZ-2F R/B* 2016-057B 29/09/2016 5500 42.78 CZ-2F R/B 2016-061B 04/11/2016 5500 42.77 CZ-7 R/B 2017-021B 18/05/2017 6000 42.76

Large catalogued intact objects with mass > 5000 kg 14 rocket bodies (∼4% of large re-entered rocket bodies) 3 spacecraft (∼4% of large re-entered spacecraft) 1-2 intact objects per year

Average re-entries per year

4 rocket bodies < 1 spacecraft 4-5 intact objects

* Used to launch Tiangong-1 * Used to launch Tiangong-2

3

1 1

6

4 3

5 5

9

3

1 1 1 1

3

1 1

7

5

3

6 6

9

3

0

2

4

6

8

10

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017Num

ber o

f re-

ente

red

obje

cts w

ith m

ass >

39

00 k

g

R/B SC R/B+SC

Re-entered mass [2008-2017]

8140 8332 8909 18985 22851 22139 21413 19799

12190 10496

60585 64075 52812

102895

79620 66942

86542

70194

99777

61195

68725 72407 61721

121880

102471 89081

107955

89993

111967

71691

0

20000

40000

60000

80000

100000

120000

140000

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Re-e

nter

ed m

ass [

kg]

SC R/B R/B+SC

5502 6100

38902

5502 5502

26300

6000 5668

13525

7289

0

10000

20000

30000

40000

50000

2008 2009 2010 2011 2012 2013 2014 2015 2016 2017

Re-e

nter

ed m

ass [

kg] R/B SC

Phobos-Grunt UARS Progress-M 27M

1 SL-16, 2 SL-23, 2 CZ-2F

Mass > 500 kg

Mass > 5000 kg

LARGE M > 50 kg

LARGE M > 500 kg

LARGE M > 5000 kg

No. Mass [kg]

No. Mass [kg] No. Mass [kg]

Rocket bodies

366 754 142 (83%)

324 744 637 (83%)

14 93 808 (78%)

Spacecraft 82 157 098 (17%)

68 153 254 (17%)

3 26 482 (22%)

Intact objects

448 911 240 392 897 891 17 120 290

Orbital inclination of intact objects re-entered between 2008 and 2017

392 intact objects with mass > 500 kg

70 18%

29 7%

0 0%

76 19%

108 28%

19 5%

11 3%

45 11%

14 4%

20 5% > 90°

80°-90°

70°-80°

60°-70°

50°-60°

40°-50°

30°-40°

0

20

40

60

80

100

120DE

LTA

2 R/

BM

OLN

IYA

3-43

DELT

A 2

R/B

CZ-4

B R/

BSL

-8 R

/BSL

-4 R

/BCZ

-2C

R/B

CZ-4

B R/

BSL

-4 R

/BCZ

-4B

R/B

JB-3

BM

OLN

IYA

1-44

MO

LNIY

A 3-

45SL

-8 R

/BSL

-4 R

/BSL

-3 R

/BCO

SMO

S 12

22SL

-4 R

/BSL

-4 R

/BPR

OG

RESS

-M 2

7MM

OLN

IYA

1-42

MO

LNIY

A 1-

92SL

-6 R

/B(1

)SL

-6 R

/B(2

)SL

-6 R

/B(2

)SL

-6 R

/B(2

)RO

SAT

SL-6

R/B

(2)

MO

LNIY

A 3-

46U

ARS

CZ-3

C R/

BSL

-26

R/B

SL-4

R/B

SL-4

R/B

SL-4

R/B

SL-4

R/B

SL-1

2 R/

B(1)

SL-4

R/B

SL-4

R/B

SL-4

R/B

SL-4

R/B

SL-4

R/B

SL-4

R/B

SL-4

R/B

ANTA

RES

R/B

SL-4

R/B

ANTA

RES

R/B

SL-2

3 R/

BCZ

-2F

R/B

CZ-2

F R/

BM

OLN

IYA

3-51

DELT

A 2

R/B(

1)CZ

-3A

R/B

DELT

A 4

R/B

CZ-3

B R/

BCZ

-3B

R/B

CZ-3

A R/

BAT

LAS

3A C

ENTA

UR

R/B

ATLA

S 2A

S CE

NTA

UR

R/B

ATLA

S 5

CEN

TAU

R R/

BG

SLV

R/B

CZ-3

C R/

BAR

IAN

E 44

L R/

BAR

IAN

E 44

L R/

BAV

UM

R/B

ARIA

NE

5 R/

B

Orb

ital i

nclin

atio

n [d

eg]

65 62 60 51 51 51 51

43 43 43 43 43 43 43 42 41 34

010203040506070

PRO

GRE

SS-M

27M

PHO

BOS-

GRU

NT

UAR

SSL

-16

R/B

SL-2

3 R/

BSL

-23

R/B

SL-2

3 R/

BCZ

-2F

R/B

CZ-2

F R/

BCZ

-2F

R/B

CZ-2

F R/

BCZ

-2F

R/B

CZ-2

F R/

BCZ

-7 R

/BCZ

-2F

R/B

CZ-7

R/B

DRAG

ON

/FAL

CON

9

Orb

ital i

nclin

atio

n [d

eg]

17 intact objects with mass > 5000 kg Mass > 500 kg

> 90° 70 18% 80°-90° 29 7% 70°-80° 0 0% 60°-70° 76 19% 50°-60° 108 28% 40°-50° 19 5% 30°-40° 11 3% 20°-30° 45 11% 10°-20° 14 4% 0°-10° 20 5%

Latitude bands overflown by re-entered objects [2008-2017]

0102030405060708090

100

DELT

A 2

R/B

MO

LNIY

A 3-

43DE

LTA

2 R/

BCZ

-4B

R/B

SL-8

R/B

SL-4

R/B

CZ-2

C R/

BCZ

-4B

R/B

SL-4

R/B

CZ-4

B R/

BJB

-3 B

MO

LNIY

A 1-

44M

OLN

IYA

3-45

SL-8

R/B

SL-4

R/B

SL-3

R/B

COSM

OS

1222

SL-4

R/B

SL-4

R/B

PRO

GRE

SS-M

27M

MO

LNIY

A 1-

42M

OLN

IYA

1-92

SL-6

R/B

(1)

SL-6

R/B

(2)

SL-6

R/B

(2)

SL-6

R/B

(2)

ROSA

TSL

-6 R

/B(2

)M

OLN

IYA

3-46

UAR

SCZ

-3C

R/B

SL-2

6 R/

BSL

-4 R

/BSL

-4 R

/BSL

-4 R

/BSL

-4 R

/BSL

-12

R/B(

1)SL

-4 R

/BSL

-4 R

/BSL

-4 R

/BSL

-4 R

/BSL

-4 R

/BSL

-4 R

/BSL

-4 R

/BAN

TARE

S R/

BSL

-4 R

/BAN

TARE

S R/

BSL

-23

R/B

CZ-2

F R/

BCZ

-2F

R/B

MO

LNIY

A 3-

51DE

LTA

2 R/

B(1)

CZ-3

A R/

BDE

LTA

4 R/

BCZ

-3B

R/B

CZ-3

B R/

BCZ

-3A

R/B

ATLA

S 3A

CEN

TAU

R…AT

LAS

2AS

CEN

TAU

R…AT

LAS

5 CE

NTA

UR

R/B

GSL

V R/

BCZ

-3C

R/B

ARIA

NE

44L

R/B

ARIA

NE

44L

R/B

AVU

M R

/BAR

IAN

E 5

R/B

Latit

ude

band

s ove

rflo

wn

[deg

]

> 80° > 70° > 60° > 50° > 40° > 30° > 20° > 10°

24% 25%

45%

72% 77% 80% 91% 95%

392 intact objects with mass > 500 kg

Source: http://www.aerospace.org

34 sightings (27 rocket bodies and 7 spacecraft) out of 373 re-entries of large intact objects (299 rocket bodies and 74 spacecraft) between 2010 and 2017: i.e. in ∼9% of the re-entry events

Moreover, also the re-entry of the Cygnus mass simulator (3800 kg) was sighted in 2013

Sightings [2010-2017]

1 2 1 4

7 8

6

5

2010 2011 2012 20132014 2015 2016 2017

0

20

40

60

80

100

120

SL-4

R/B

DELT

A 2

R/B(

2) (P

AM-D

)

SL-4

R/B

ARIA

NE

44L

R/B

COSM

OS

1484

SL-4

R/B

CZ-4

B R/

B

GO

CE

CZ-3

B R/

B

COSM

OS

1220

SL-4

R/B

COSM

OS

1400

SL-3

R/B

SL-4

R/B

FALC

ON

9 R

/B

CZ-4

B R/

B

SL-4

R/B

SL-6

R/B

(2)

SL-4

R/B

COSM

OS

1315

NFI

RE

SL-4

R/B

SL-4

R/B

SL-2

3 R/

B

CZ-3

B R/

B

JB-3

A

SL-4

R/B

CZ-7

R/B

FALC

ON

9 R

/B

CZ-7

R/B

CZ-4

B R/

B

SL-4

R/B

SL-4

R/B

ANTA

RES

R/B

Orb

ital i

nclin

atio

n [d

eg]

2011

2011

2012

2013

2013

2013

2013

2014

2014

2014

2014

2014

2014

2014

2015

2015

2015

2015

2015

2015

2015

2015

2016

2016

2016

2016

2016

2016

2017

2017

2017

2017

2017 2010

1. A steel propellant tank and 2 titanium pressure spheres – identified as debris from 2nd stage of Delta II 2. Several metal objects - probably debris from 3rd stage of GSLV 3. A titanium rocket-motor casing - identified as debris from 3rd stage of Delta II 4. A metallic sphere - probably a helium pressure tank from 2nd stage of Zenit 3F 5. A metallic sphere - probably a helium pressure tank from 3rd stage of Ariane 4 6. Two metallic spheres - probably helium pressure tanks from 3rd stage of CZ-4B 7. A propellant tank - probably from 2nd stage of a Delta 8. Small cylindrical tanks and a metal ring - probably from the 2nd stage of Falcon 9 9. Two small spherical tanks - probably from the 2nd stage of Zenit 3F 10. A composite overwrapped pressure vessel - identified as a pressure vessel from the 2nd stage of Falcon 9 11. A composite overwrapped pressure vessel - believed to belong to the Vega upper stage AVUM 12. “Several” fuel tanks from the 2nd stage of Zenit 3F

13. Three spherical tanks were found in the Spanish towns of Calasparra, Villavieja and Elda in November 2015 (identified as objects from a Centaur upper stage used to launch the spacecraft USA 200 - 2008-010A - on March 13, 2008) – no TLEs and decay time available

(1)

Recovered re-entry debris (http://www.aerospace.org/cords/research/reentry-data) 20

09-0

52C

2007

-037

B

2003

-058

C

2011

-001

C

1997

-016

C

2012

-021

C

1975

-077

B

2014

-052

B

2015

-074

C

2016

-050

B

2012

-006

K

2017

-086

D

2010

Mongolia Asia

Malawi Africa

2011 2011 2011

Artigas Uruguay

Baggs Wyoming

USA Mata Roma

Brazil

2012 2013

Buna Texas USA

2013

Ngezi Zimbabwe

Africa

2014 2016 2016 2016 2018

Santa Rita do Pardo Brazil Tuyen Quang

Province Vietnam

Giliraja East Java Indonesia

Oddanchatram India

1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

Puno region Peru

What to expect in 2018? What has already happened?

What is going to happen?

Uncontrolled re-entry, on 27 January 2018, of the Zenit-2SB second stage 2017-086D, with an empty mass of 8307 kg

Uncontrolled re-entry of the Chinese space station Tiangong-1, with a launch mass of 8500 kg

Uncontrolled re-entry, on 8 February 2018, of the C-25 cryogenic upper stage 2017-031B of the GSLV-MK3-D1 launcher, with a dry mass of ∼5300 kg

The re-entry of the Zenit-2SB second stage The fourth launch, on 26 December 2017, of the Russian-Ukrainian expendable carrier rocket Zenit-3SLBF (or Zenit-2SB/Fregat-SB) put into orbit the Angola’s first geostationary communication satellite AngoSat-1

After separating from the Fregat upper stage, the Zenit-2SB second stage began its orbital decay, only subjected to natural perturbations, from an initial orbit of ∼162 × 566 km in altitude and inclination of 51.37°

Physical characteristics of the Zenit-2SB second stage

COSPAR ID 2017-086D Cat. Number 43090

Zenit-2SB second stage

Length 10.4 m

Diameter 3.9 m

Inert mass 8307 kg

Observed orbital decay

The re-entry of the Zenit-2SB second stage Evolution of the ballistic parameter

0.006000.006500.007000.007500.008000.008500.009000.009500.01000

19.7

13.2

10.8 9.2

5.9

4.0

3.0

1.7

1.1

0.3

0.2

Balli

stic

par

amet

er

[m^2

/kg]

Residual lifetime [days]

<B> = 0.00881 m2/kg σ ∼ 7%

11.8 14.4

2.5 -0.1 1.2

-4.8 -8.4

-11.0 -11.9

-4.4 -6.8

-15-10

-505

101520

19.7

13.2

10.8 9.2

5.9

4.0

3.0

1.7

1.1

0.3

0.2

Perc

enta

ge e

rror

on

re

-ent

ry p

redi

ctio

ns [%

]

Residual lifetime [day]

Percentage error affecting the estimate of the residual lifetime Mean prediction error

7.0 6.6

5.7 6.1

6.9

7.9 8.5 8.5

7.7

5.6

6.8

4

5

6

7

8

9

19.7

13.2

10.8 9.2

5.9

4.0

3.0

1.7

1.1

0.3

0.2M

ean

pred

ictio

n er

ror [

%]

Residual lifetime [days]

Orbital predictor SATRAP Atmospheric density model NRLMSISE-00

MACB D=

100 PRED REFRL

REF IN

T TPET T

−= ×

−1

PNRL

n P

PEMPE

N=

= ∑

Value used for the post-event assessment

11 re-entry predictions

A post-event assessment

The re-entry of the Zenit-2SB second stage Re-entry uncertainty windows Residual lifetime ± 30% - re-entry predictions 1-7 Residual lifetime ± 20% - re-entry predictions 8-11 & post-event assessment Reference re-entry epoch: 27 January 2018, 23:32 UTC (JSpOC post-event assessment)

-5

0

5

10

19.7 13.2 10.8 9.2 5.9 4.0 3.0 1.7 1.1 0.3 0.2Days

with

resp

ect t

o th

e

refe

renc

e re

-ent

ry

epoc

h

Residual lifetime [days]

START COIW END

-0.6

-0.4

-0.2

0

0.2

1.7 1.1 0.3 0.2Residual lifetime [days]

START COIW END

9

11 10

8 9 TLE: 26 January 2018, 05:49 UTC, Residual lifetime = 41h 42m

TLE: 26 January 2018, 21:58 UTC, Residual lifetime = 25h 34m

COIW - 27 January 2018, 20:29 UTC COIW - 27 January 2018, 18:56 UTC

8

The re-entry of the Zenit-2SB second stage

10 11

TLE: 27 January 2018, 15:31 UTC, Residual lifetime = 8h 1m TLE: 27 January 2018, 19:52 UTC, Residual lifetime = 3h 40m

Post-event assessment TLE: 27 January 2018, 19:52 UTC

B = 0.0077 m2/kg

Nominal re-entry epoch 27 January 2018, 23:32 UTC

Re-entry window: ±0.03 days ± 43m12s

Latitude: -8.38°

Longitude: 285.01°

COIW - 27 January 2018, 23:17 UTC COIW - 27 January 2018, 23:11 UTC

The re-entry of the Zenit-2SB second stage

JSpOC decay epoch 27 January 2018, 23:32 UTC ± 1 min Lat: -9.2° Lon: 285.7°

Source: Aerospace Corporation

«This object was sighted re-entering on 27 January 2018 at 23:32 UTC over Pucallpa, Peru»

«Several fuel tanks were recovered by the Peruvian Air Force near the Puno region of Peru after they were notified by local residence»

Sighting

Recovered debris

© Peruvian Air Force / AFP

Re-entry of the C-25 cryogenic upper stage The Indian Geosynchronous Satellite Launch Vehicle Mark III D1 (GSLV-MK3-D1) was used to launch the experimental Indian geostationary communication satellite GSAT-19 on 5 June 2017

After releasing the spacecraft, the upper stage remained passive in a geosynchronous transfer orbit

COSPAR ID 2017-031B Cat. Number 42748

C-25 Cryogenic upper stage

Length 13.55m

Diameter 4 m

Inert mass ∼5300 kg

10

100

1000

10000

100000

0.0

10.9

21.0

26.8

35.2

43.5

48.5

56.0

60.6

66.4

79.3

86.0

93.4

109.

111

9.0

128.

314

0.8

149.

815

9.8

175.

818

2.6

184.

919

0.3

203.

721

2.3

215.

421

9.4

225.

323

3.7

239.

724

4.1

245.

124

6.3

247.

1

Perigee altitude [km] Apogee altitude [km]

First TLE: 5 June 2017, 07:18 UTC 160 × 34918 km; inc: 21.55°

Last TLE: 7 February 2018, 19:17 UTC 101 × 1484 km; inc: 21.42°

Observed orbital decay

JSpOC decay epoch 8 February 2018, 11:30 UTC ± 180 min Lat: 21.1° Lon: 341.9°

Sub-satellite ground tracks corresponding to the last JSpOC re-entry uncertainty window

The Chinese space station Tiangong-1 Tiangong-1, launched on 29 September 2011, was the first Chinese space station, used both as human tended laboratory and target for testing orbital rendezvous and docking

Launch mass 8506 kg

Propellant at launch 1000 kg

Consumables at launch ≈ 350 kg

Current propellant* ≈ 350 kg

MMH ≈ 120 kg

N2O4 ≈ 230 kg

Current consumables** ≈ 50 kg

Current mass# ≈ 7550 kg

Dry mass ≈ 7150 kg

**Food, food packaging, water and oxygen consumption for 57 astronaut-days: ≈ 303 kg

* Propellant consumption from manoeuvre sequence: ≈ 650 kg

# Comparable to the launch mass of Progress-M 27M (7289 kg)

Status of Tiangong-1 The ground control of the space station was lost on 16 March 2016

The autonomous on board attitude control remained, and still is, operational. According to China Manned Space Agency (CMSA): «Its attitude kept stabilized and no anomaly occurred» http://en.cmse.gov.cn/col/col1763/index.html

The attitude is controlled through reaction wheels and reaction control thrusters

Probably , the solar panels are kept pointed towards the Sun to guarantee the power supply needed to keep the station alive, and the body is aligned along the velocity vector

The attitude control has an indirect effect on the orbit by varying the effective drag cross-section by producing a net ∆V when the reaction control

thrusters are activated

As an example, possible recent thrusting periods were identified in the TLEs of January 27, February 2 and February 11

For instance, the net orbital effect of the thrusting occurred on 27 January 2018 corresponded to a ∆V of a few meters per second

Maneuver day B* da dt

a e i ω

January 27 X X X X

February 2 X X X X X

February 11 X X X X X

Significant manoeuvres occurred from 20 January to 18 February 2018

January 27

February 2

February 11

January 27

February 2

February 11

Environmental conditions

Some minor geomagnetic storms (4 < KP ≤ 5)

Quite low solar activity levels

Estimate of the Tiangong-1 ballistic parameter

0.0055

0.0060

0.0065

0.0070

0.0075

0.0080

0.0085

8.47

11.2

1

15.1

6

17.1

6

18.7

7

22.1

5

24.0

8

25.0

9

26.0

2

29.2

7

29.5

7

31.2

6

32.5

0

35.6

2

38.1

2

43.0

8

47.1

4

50.1

3

51.1

2

52.1

2

53.1

7

Balli

stic

par

amet

er [m

²/kg]

Prediction epoch [day of 2018]

NRL-B -50/60 GOST-B-50/60 NRL-B-30 GOST-B-30

NRL-B-20 GOST-B-20 NRL-B-10 GOST-B-10

Forecasting the Tiangong-1 re-entry epoch

80

82

84

86

88

90

92

94

96

98

100

8.47

11.2

1

15.1

6

17.1

6

18.7

7

22.1

5

24.0

8

25.0

9

26.0

2

29.2

7

29.5

7

31.2

6

32.5

0

35.6

2

38.1

2

43.0

8

47.1

4

50.1

3

51.1

2

52.1

2

53.1

7

Nom

inal

re-e

ntry

epo

ch a

t 80

km [d

ay o

f 201

8]

Prediction epoch [day of 2018]

NRL-B -50/60 GOST-B-50/60 NRL-B-30 GOST-B-30

NRL-B-20 GOST-B-20 NRL-B-10 GOST-B-10