Journal of Robotics, Networking and Artificial Life, Vol. 5, No. 2 (September 2018) 101-104___________________________________________________________________________________________________________Dynamics Analysis of Payload On-orbit Catapult Separation Based on ADAMSYi Li, Yingmin Jia*, Jianheng Ling

The Seventh Research Division and the Center for Information and Control
School of Automation Science and Electrical Engineering
Beihang University (BUAA), 37 Xueyuan Road, Haidian District
Beijing, 100191, China
E-mail: liyi309@163.com; ymjia@buaa.edu.cn; lingjianheng1987@163.com
www.buaa.edu.cn

Abstract
In this paper, a catapult separation device equipped with guide mechanism is considered, and the corresponding
dynamic model is descripted firstly. Then, employing the dynamic simulation software ADAMS, the virtual
prototype model of the separation device is established, and the whole process of on-orbit separation is simulated.
Finally, the structure parameters of the guide mechanism such as the number of roller group or distance between
groups are studied. The simulation results could provide references for the optimization of the separation device.
Keywords: Guide mechanism, catapult separation, virtual prototype, angular velocity.

force in the process of catapult separation. The
additional torque introduced by the eccentric separation
would affect the attitude or even cause tumbling of thepayload, so it is very important to study the separation
dynamics of eccentric payload. Jeyakumar2 establishedthe dynamic equations for the satellite separation systemusing the helical compression spring mechanism. In
Jiang’s research3, characteristics of the constrained andcentroid biased on-orbit satellite separation wereanalyzed, and then the dynamic model of the separating
motion was formulated. Based on multi-body dynamic
theory, Shen4 built the eccentric separation model, andsimulated the dynamic during the separation by
ADAMS software. Zhang5 built virtual prototype modelof separation mechanism to simulate the whole processof payload on-orbit launch, and analyzed the stability ofon-orbit launch considering the influence of separation
mechanism error. Shu6 focused on the multi-bodydynamics during separation/release, and established the1. Introduction
On-orbit separation refers that satellite platform
separates payload with a separation device, and thepayload enters its preset orbit successfully1. The
common schemes for on-orbit separation include
pyrotechnic separation, electromagnetic separation andcatapult separation. Pyrotechnic separation has security
problem since the separation process with explosive
material would produce large impact and interference
on onboard devices; electromagnetic separation requires
more power consumption, meanwhile, it's easily
influenced by external magnetic field; however, catapult
separation has the following advantage: simple structure,less power consumption and easy to control, therefore,
the catapult separation is chosen in this paper.
Due to the deviations of compressing springparameters, machining errors or external disturbances,the mass center of the payload is not on the resultant*

Corresponding author

Copyright © 2018, the Authors. Published by Atlantis Press.
This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-nc/4.0/).
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Journal of Robotics, Networking and Artificial Life, Vol. 5, No. 2 (September 2018) 101-104___________________________________________________________________________________________________________2.2. Dynamics description

simulation model based on ADAMS. The above
researches stressed on dynamics analysis of tube-shapeeccentric sub-satellite separation, and analyzed theinfluences of separation mechanism parameters on
satellite platform by employing MATLAB or ADAMS
platform. On basis of the previous studies, in this paper,a new type of catapult separation device equipped withguide mechanism is presented, and the influences of theguide mechanism's parameters on the payload attitude
are analyzed in ADAMS/View.

During the process of catapult separation, the separation
impulse is provided by release of the energy stored in
the compressing springs. Based on the structure of theseparation device, the force of the payload include
spring force and the contact force produced by therollers. By means of multi-body dynamics theory, theforce and the moment of payload are analyzed andcalculated as follows:
nnki 1i 1

j 1

F   Fli   Fri   FSj ,2. Problem Formulationnni 1i 1(1)M  Rbr ( rli  Fli   rri  Fri

2.1. Description of catapult separation device

kAs shown in Fig. 1, the catapult separation device
includes driving motors, differential gear mechanism,
four compression springs, the guide mechanism, a carused for loading the payload, and so on. The guidemechanism consisting of rollers plays a crucial role inrestraining angular velocity of the payload. According
to the general design scheme, the whole separation
process can be divided into three phases as follows:(i) the payload moves together with the car, in otherwords, they maintain relative static,(ii) the car collides with the buffers in the end of wholedistance, the payload moves along the guidemechanism under the effect of inertial force, andthe payload is still not out of the car in this phase,(iii) the payload is completely out of the guidemechanism’s constraints, that means the car and thepayload move respectively.

  rSj  FSj ).

(2)

j 1

where Fli , Fri are the contact forces of the i th group of
the rollers, and FSj is the spring force of the j th spring.
Rbr is transformation matrix, from inertia reference
coordinate system to the payload coordinate system. rli ,rri and rS j are the position vectors mapped in inertia
reference coordinate system.
Based on Hertz contact theory, the nonlinear spring
damping contact model is adopted to model the contactforce which can be expressed as F    F0   K  li  C lili  (3)Fli   Ni   ,  FNi
 Fsi  
where FNi represents the normal pressure, Fsi
represents the friction force. F0 is the preload, C andK represent the damping factor and equivalent system
stiffness, respectively, li denotes the normal
deformation and  satisfies
 sign(v)   f , v  v f   step ( v , v f ,  f , vs ,  s )  sign(v) , vs  v  v f
 step(v, v ,  , v ,   ), v  v
sssss


(4)

where  f states the dynamic frictional coefficient, ands represents the static frictional coefficient. v is thevelocity of the payload, v f denotes the dynamic slip
velocity while vs denotes the static slip velocity.
Fig. 1. Schematic drawing of the catapult separation device

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Journal of Robotics, Networking and Artificial Life, Vol. 5, No. 2 (September 2018) 101-104___________________________________________________________________________________________________________

3. Virtual Prototype Modelingdifferent conditions, we can optimize and redesign theguide mechanism.
We assume that the initial angular velocity of thesatellite platform is zero, and the orbit motion of thepayload is neglected in the process. The mass of theplatform is M  500kg , the mass of the payload ism  5kg ; the stiffness coefficients of four compression
springs are set as k1  2.43N / mm , k2  2.46 N / mmk3  2.47 N / mm k 4  2.48 N / mm respectively; thespring stroke length is  x  90 mm (the velocity of thecar will be 4m / s ), the gravity is neglected; and thesimulation time is 0.1s , the step is 200, the lock isreleased at t  0.034 s , otherwise.
The guide mechanism primitively has two groups ofrollers, and now we add one group of rollers between
the two groups on the premise of little change of theseparation velocity as shown in Fig. 3, the distance
between the added group and the first group is set asl  75mm .

Using the ADAMS software, the virtual prototype
model including the satellite platform, the payload andthe catapult separation device is established as shown in
Fig. 2. In general, there is a constraint relationshipknown as joint between two components, this model has
three kinds: Fixed joint, Revolute joint, andTranslational joint.

Fig. 2.Virtual prototype model of separation system

Then, we should define force, torque, and contact
for the virtual prototype model. The defined contacts aredemonstrated in Table 1, calculating for which there are
two methods: Restitution method and Impact method.
According to the dynamics analysis in chapter 2, weadopt the Impact method in this model.

lTable 1. Contacts of the model
added group

Schedule

Rigid 1

Rigid 2

Contact 1
Contact 2
Contact 3
Contact 4
Contact 5
Contact 6

carcarroller_11
roller_12
roller_21
roller_22

payloadbufferpayloadpayloadpayloadpayloadFig. 3. Installation of the groups of rollers

Fig. 4 shows the final roll angular velocity (rotationabout x axis) decreases from 0.849°/s to 0.553°/s, theyaw angular velocity (rotation about y axis) decreases
from 1.063°/s to 0.870°/s, and the pitch angular velocity(rotation about z axis) decreases from0.594°/s to 0.4°/s
after adding one group of rollers. So adding groups ofrollers on the premise of little change of the separation
velocity could restrain the separation angular velocity.
Considering the guide mechanism has three groupsof rollers, we try to adjust the distance between themiddle group and the first group, that is, the distance isimplemented at l1  50mm , l2  35mm , respectively.
The simulation results are illustrated in Fig. 5.

4. Simulation
The payload’s angular velocity is the main target ofmeasuring the stability of on-orbit catapult separation.
Many factors influence the separation angular velocity,
including various structure parameters of the device andthe motion of the satellite platform. Here, the structure
parameters of the guide mechanism are discussed. By
analyzing the influence rules of the parameters under103

Journal of Robotics, Networking and Artificial Life, Vol. 5, No. 2 (September 2018) 101-104___________________________________________________________________________________________________________

When the distance decreases to 50 mm, the angularvelocities including roll, yaw and pitch decrease as well(the roll angular velocity decreases to 0.280°/s, the yaw
angular velocity decreases to 0.353°/s and the rollangular velocity decreases to 0.327°/s); however, if thedistance continues to decrease to 35 mm, the angularvelocities will increase instead.
5. Conclusion
In this paper, a new type of catapult separation device
equipped with guide mechanism is considered; using theADAMS software, the virtual prototype model isestablished. The simulation results show that adding one
group of rollers and adjusting it to the center of theother two groups could restrain the angular velocity
effectively.

Fig. 4. The angular velocity after adding one group of rollers

Acknowledgements
This work was supported by the National Basic
Research Program of China (973 Program:
2012CB821200, 2012CB821201), the NSFC (61327807,61520106010, 61134005, 61521091).
References
1. J. P. Yuan, et al. Spacecraft Counter Orbit Dynamics(China Astronautic Publishing House, 2014).
2. Jeyakumar. D, B. N. Rao. Dynamics of satellite
separation system, J. Sound Vib., 297(1), 2006, pp.
444-455.
3. C. Jiang, Z. K. Wang, L. Fan, et al. Dynamics analysis of
the constrained and centroid biased on-orbit satellite
separation (in Chinese), Flight Dyn., 28(1), 2010, pp.
76-79.
4. X. F. Shen, Y. Z. Xiao, et al. Dynamic simulation ofeccentric sub-satellite based on Monte Carlo method (inChinese), Aerospace Shanghai, 31(1), 2014, pp. 12-17.
5. L. Zhang, Y. Liao and G. Tang. Dynamic simulation of
payload on-orbit launch (in Chinese), J. Projectiles
Rockets Missiles Guid., 28(4), 2008, pp. 186-189.
6. Y. Shu and Z. Li. Dynamics simulation of on-orbit
release and separation of payload (in Chinese),
Spacecraft Environment Eng., 29(1), 2012, pp. 18-22.
7. Nohmi M, Tanikawa J and Hosoda T. Simulation
analysis of a tethered space robot for space experiment on
sounding rocket by JAXA/ISAS, in Proc. Int. Conf.
Mechatronics and Automation. IEEE, China, Xi’an,
2010, pp. 264-269.
8. Nenchev D N, Nohmi M and Uchiyama M. Tethered
robot casting using a spacecraft-mounted manipulator, J.
Guid. Contr. Dyn., 24(4), 2001, pp. 827-833.

Fig. 5. The angular velocity with different distances104