C-3
Parabolic Flight Micro-Gravity Experiment of Tethered Recovery
in Tethered Sampling Method
Tomio Yamanaka, Ken Fujiwara, Masaki Maeno, Junichi Nishida and Saburo Matunaga
(Tokyo Institute of Technology)
Hajime Yano, Koji Nakaya and Osamu Mori
1. Introduction
The Japanese asteroid probe, HAYABUSA (Fig. 1.1), was launched and succeeded in rendezvous with the asteroid “ITOKAWA” in December 2005 and tried to collect sample by touching down. HAYABUSA’s sampling method was the bullet shooting method as shown in Fig. 1.2. The method can get a few hundred milligrams sample on the surface of the asteroid. For the next minor-body sample return mission, the sample collection which keeps depth information is required to investigate the inner structure of the asteroid. And getting much more sample quantity is also desired.
Fig. 1.1 HAYABUSA (cJAXA)
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Fig. 1.2 HAYABUSA’s Sampling Method (cJAXA)
The tethered sampling method is a new sampling method proposed by the authors to satisfy the requests for next minor-body sample return mission [1-3]. It has three phases, 1) a corer connected with tether is shot to penetrate the surface of a minor-body, 2) the corer is pulled up with the tether using a reel mechanism and 3) the corer is recovered into a storage box (as shown in Fig. 1.3).
リール機構格納庫ピストン二重円筒ホーンcorerstoragehornejectorReel mechanism(a) Shoot(b) Insert/Collect(c) Pull/Recoverytether
Fig. 1.3 Tethered Sampling Method
Pulling out and recovery phase were focused on in this research. Fundamental experiments under micro-gravity using a free fall capsule were previously conducted by authors [4-5]. But there are some disadvantages in experimental duration and space in the free fall capsule way. Experimental duration, about 4.5 seconds, is too short to observe a behavior of the corer and tether in retrieval phase. And experimental area in the capsule is too small to mount a full size sampler horn. So, the micro-gravity experiments using parabolic flight were necessary to conduct experiments under more realistic conditions. In this paper, the experimental setup, parameters and results are explained.
2. Experimental Setup
Micro-gravity experiments using parabolic flight were conducted to check the feasibility of the corer and tether retrieval. 38 experiments were conducted in total, and the validated data were obtained in 27 of them. In the experiment, the duration of micro-gravity was about 20 seconds and gravity level was 1/100G order.
The experimental setup used in the experiments consists of a reel mechanism, a shutter mechanism and a corer holder, as shown in Fig. 2.1. Five video cameras are also installed. Two of them are located in front of the experimental area for stereovision. Another two of them are located at the upside and lower side of the experimental area. The other camera is located at the side of the reel mechanism. The size of the experimental area is 660mm*560mm*700mm. The tether is in the initial, and each experiment is ended when the corer reaches a storage box. A photograph of the experimental setup is shown in Fig. 2.2. The experimental area is in the left rack and control devices are in the right rack.
Fig. 2.1 Pattern Diagram (Left Side Rack)
Reel mechanismShutter mechanismComputerReel controllerCorer holderSampler horn
Fig. 2.2 Experimental Setup
The reel mechanism which is necessary to pull up and retrieve the corer is shown in Fig. 2.3.
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Motor 2Motor 1Tension Sensor 1Tension Sensor 2Rotary EncoderGuide RollerSpool
Fig. 2.3 Overview of Reel Mechanism
It consists of two motors, two rotary encoders, two tension sensors and a guide roller. Motor 1 and motor2 are connected directly with the spool part and the guide roller respectively. The guide roller divides tether tension into outer tension and inner tension as shown in Fig. 2.4. Keeping the inner tension positive prevents tether from getting entangled. The tension sensor 1 measures twice of the inner tension and the sensor 2 measures the outer tension. These measurements value are fed back in the motor control. Each motor driver has two control modes: one is a current mode and the other is a voltage mode.
Tension Sensor 1CorerMotor 1TetherGuide RollerRotary EncoderSpoolTension Sensor 2Inner Tension
Fig. 2.4 Pattern Diagram of Reel Mechanism
As initial condition, the corer is in the corer holder, as shown in Fig. 2.5, on the assumption that the corer is inserted into the minor-body. The corer is fixed by a sponge inside the corer holder. Pulling out angle can be changed, as shown in Fig. 2.6. Corer HolderSponge
Fig. 2.5 Corer Holder
θ= 0deg.θ= 30deg.θ= 60deg.
Fig. 2.6 Pulling Out Angle
3. Experimental Parameters
The experimental parameters are following below,
?? Two types of pulling out force
?? Four types of initial conditions combined corer position and pulling out angle
?? Three types of tether retrieval speed
?? Three types of motor control laws
Pulling out force can be changed by using single corer and dual corer. The dual corer consists of outer and inner cylinders, as shown below. Pulling out force of the dual corer is smaller than that of the single corer because the outer cylinder prevents pressure on the inner one. Pulling out mechanism using the dual corer is illustrated in Fig. 3.2.
Fig. 3.1 Dual Corer
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Reel mechanismInner corerOuter corer
Fig. 3.2 Pulling Out with Dual Corer
Fig. 3.3 shows the four types of initial conditions of the corer.
?? Pulling out angle: 0 deg.
Position: Beneath the sampler horn
?? Pulling out angle: 30 deg.
Position: Beneath the sampler horn
?? Pulling out angle: 60 deg.
Position: Near the sampler horn
?? Pulling out angle: 60 deg.
Position: Away from the sampler horn
Sampler HornCenter 0deg.Center 30deg.Distant Location 60deg.Outside 60deg.70cm55cm30cm17cm
Fig. 3.3 Corer Initial Arrangements
There are three types of tether retrieval speeds, low (0.06m/s, 0.07m/s), middle (0.1m/s) and high (0.15m/s). The motor control laws for constant velocity are the followings,
・ Feed back PID control (current input mode)
・ Feed back P control (voltage input mode)
・ Constant command control (voltage input mode)
4. Results
Fig. 4.1 and 4.2 show the result of the experiments affected by pulling up force. The graph represents the inner tension, outer tension and retrieval speed. The common parameters of both of the experiments are the followings,
・ Retrieval speed: Middle (0.1m/s)
・ Pulling out angle: 60deg.
・ Position: Away from the sampler horn
According to these figures, pulling out motion is detected at approximately 2 seconds and pulling out force of dual corer and single corer are about 0.4N and 6.8N respectively. The motion of the corer indicates that strong pull out force causes increase of the number of corer impact on inside the sampler horn. Sample becomes less and less as the number of corer impact more increases.
Ex.2-06 Dual Corer, Middle Speed (0.1m/s), Outside 60 deg.00.020.040.060.080.10.120.140.160.180.20123456789Time [sec]Speed [m/s]012345678Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.1 Small Pulling Out Force (Dual Corer)
Ex.2-09 Single Corer, Middle Speed (0.1m/s), Outside 60 deg.00.020.040.060.080.10.120.140.160.180.20123456789Time [sec]Speed [m/s]012345678Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.2 Large Pulling Out Force (Single Corer)
Fig. 4.3 to 4.5 show the result of the experiments affected by initial conditions of the corer: 0 deg. beneath the horn, 30 deg. beneath the horn and 60 deg. near the horn. The common parameters of these experiments are the followings,
・ Pulling up force: Small (dual corer)
・ Retrieval speed: High (0.15m/s)
According to the these experiments, it is found that the corer can be recovered even if it is placed outside of the sampler horn and it is inserted sidlingly beneath the horn.
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Ex.1-05 Dual Corer, High Speed (0.15m/s), Center 0 deg.00.020.040.060.080.10.120.140.160.180.200.511.522.533.544.555.56Time [sec]Speed [m/s]00.20.40.60.811.21.41.61.82Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.3 0 deg. Beneath the Horn
Ex.2-04 Dual Corer, High Speed (0.15m/s), Center Left 30 deg.00.020.040.060.080.10.120.140.160.180.200.511.522.533.544.555.56Time [sec]Speed [m/s]00.20.40.60.811.21.41.61.82Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.4 30 deg. Beneath the Horn Ex.2-07 Dual Corer, High Speed (0.15m/s), Outside 60 deg.00.020.040.060.080.10.120.140.160.180.200.511.522.533.544.555.56Time [sec]Speed [m/s]00.20.40.60.811.21.41.61.82Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.5 60 deg. Near the Horn
Fig. 4.6 to 4.8 show the result of the experiments affected by retrieval speed: low (0.06m/s), middle (0.1m/s) and high (0.15m/s). The common parameters of these experiments are the followings,
・ Pulling up force: Small (dual corer)
・ Pulling out angle: 30deg.
・ Position: Beneath the sampler horn
According to the camera images, it can be seen that the tether did not go soft largely and the corer did not rotate roundly when retrieval speed was almost the same as initial speed just after pulling up.
Ex.2-02 Dual Corer, Low Speed (0.06m/s), Center Left 30 deg.-0.04-0.0200.020.040.060.080.10.120.140.160.180.2012345678910111213Time [sec]Speed [m/s]00.10.20.30.40.50.60.70.80.911.11.2Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.6 Low Speed (0.06m/s)
Ex.2-03 Dual Corer, Middle Speed (0.1m/s), Center Left 30 deg.-0.04-0.0200.020.040.060.080.10.120.140.160.180.2012345678910111213Time [sec]Speed [m/s]00.10.20.30.40.50.60.70.80.911.11.2Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.7 Middle Speed (0.1m/s)
Ex.2-04 Dual Corer, High Speed (0.15m/s), Center Left 30 deg.-0.04-0.0200.020.040.060.080.10.120.140.160.180.2012345678910111213Time [sec]Speed [m/s]00.10.20.30.40.50.60.70.80.911.11.2Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.8 High Speed (0.15m/s)
Fig. 4.9 and 4.10 show the result of the experiments affected by control laws of the reel mechanism. The common parameters of both of 5
the experiments are the followings,
・ Pulling up force: Small (dual corer)
・ Retrieval speed: High (0.15m/s)
・ Pulling out angle: 0deg.
・ Position: Beneath the sampler horn
The reel mechanism was controlled by feeding back the number of spool rotations, changing the mode of the motor drivers such as current mode or voltage mode. Although big differences are not observed from the camera images in both experiments, the response and convergence of the motor driven on voltage mode are obviously much better than that of current mode from the data of the spool rotation speed.
Ex.1-05 Dual Corer, High Speed (0.15m/s), Center 0 deg.00.020.040.060.080.10.120.140.160.180.200.511.522.533.544.555.56Time [sec]Speed [m/s]00.20.40.60.811.21.41.61.82Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.9 Current Mode
Ex.4-02 Dual Corer, High Speed (0.15m/s), Center 0 deg.00.020.040.060.080.10.120.140.160.180.200.511.522.533.544.555.56Time [sec]Speed [m/s]00.20.40.60.811.21.41.61.82Tension [
N]SpeedInnerTensionOuterTensionPull OutRecovery
Fig. 4.10 Voltage Mode
5. Conclusions
In this paper, the results of the micro-gravity experiments using parabolic flights for the corer and tether retrieval in tethered sampling method are described. The experimental results indicate that the retrieval phase in tethered sampling method is feasible to work under micro-gravity.
Some improved points related to the structure and control law of the reel mechanism are found, as shown below,
1) Small pull out force enables the corer to grasp more samples because it prevents the corer from impacting on inside of the sampler horn.
2) Small pull-out force keeps reel control easy because it prevents motors from overshooting.
3) Tether recovery speed is supposed to be almost the same as the corer initial speed just after pulling out not the tether to get large slack.
References
[1] S. Matsunaga, S. Masumoto, T. Yamanaka, O.Mori, K. Nakaya, “System Discussion for Tethered Sampling Method,” 49th Symposium on Space Science and Technology, Hiroshima, 2H02, 9th-11th November, 2005, pp.6. (in Japanese)
[2] H. Yano, T. Noguchi, S. Matsunaga, O. Mori, H. Habu, S. Hasegawa, K. Kato, S. Kubota, Y. Miura, K. Nakaya, K. Nozoe, "Development of the Sampling Device for Undifferentiated Asteroid Surface and Sub-Surface Materials," Proc. 25th International Symposium on Space Technology and Science (Selected Paper), 2006-k-28, 2006, pp. 1071-1075.
[3] S. Matunaga, O. Mori, K. Nakaya, S. Masumoto and T. Yamanaka, “Concept and System Consideration of Tethered Sampling for Minorbody Exploration in Deep Space,” Proc. 25th International Symposium on Space Technology and Science (Selected Paper), 2006-k-29, 2006, pp.1076-1082.
[4] S. Matunaga, O. Mori, K. Nakaya, S. Masumoto and T. Yamanaka, “Tethered Recovery and Its Behavior of Tethered Sampling for Deep Space Minorbody Exploration,” 25th ISTS and 19th ISSFD, ISTS 2006-d-20, Kanazawa, June, 2006.
[5] S. Matunaga, T. Yamanaka, H. Ashida, J. Nishida, K. Nakaya and O. Mori, “Micro-Gravity Experiment of Reel Mechanism for Tethered Sampling Method,” Proc. 23rd Space Utilization Symposium, Vol.23, pp.109-112, 2007.
(in Japanese) 6